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	$5.45	6.158%	$5.7856	$5.79	$5.80	$5.80
Purchase #2	$227.69	5.520%	$240.2585	$240.26	$240.25	$240.30
Purchase #3	$42.44	3.540%	$43.9424	$43.94	$43.95	$43.90
Purchase #4	$116.27	13.398%	$131.8479	$131.85	$131.85	$131.80
Purchase #5	$41.78	8.135%	$45.1788	$45.18	$45.20	$45.20
Purchase #6	$82.27	7.113%	$88.1219	$88.12	$88.10	$88.10
Purchase #7	$98.65	4.672%	$103.2589	$103.26	$103.25	$103.30
7 purchase totals =	$614.55		$658.3940	$658.40	$658.40	$658.40