Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$86.84	8.788%	$94.4715	$94.47	$94.45	$94.50
Purchase #2	$242.65	5.604%	$256.2481	$256.25	$256.25	$256.20
Purchase #3	$109.79	10.844%	$121.6956	$121.70	$121.70	$121.70
Purchase #4	$78.72	10.286%	$86.8171	$86.82	$86.80	$86.80
Purchase #5	$38.54	5.574%	$40.6882	$40.69	$40.70	$40.70
Purchase #6	$109.82	12.650%	$123.7122	$123.71	$123.70	$123.70
Purchase #7	$104.42	4.516%	$109.1356	$109.14	$109.15	$109.10
7 purchase totals =	$770.78		$832.7683	$832.78	$832.75	$832.70