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	$53.68	7.706%	$57.8166	$57.82	$57.80	$57.80
Purchase #2	$91.85	9.401%	$100.4848	$100.48	$100.50	$100.50
Purchase #3	$56.75	9.490%	$62.1356	$62.14	$62.15	$62.10
Purchase #4	$151.64	5.663%	$160.2274	$160.23	$160.25	$160.20
Purchase #5	$96.62	13.188%	$109.3622	$109.36	$109.35	$109.40
Purchase #6	$47.40	10.243%	$52.2552	$52.26	$52.25	$52.30
Purchase #7	$128.52	13.787%	$146.2391	$146.24	$146.25	$146.20
7 purchase totals =	$626.46		$688.5209	$688.53	$688.55	$688.50