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	$33.50	10.774%	$37.1093	$37.11	$37.10	$37.10
Purchase #2	$226.59	12.194%	$254.2204	$254.22	$254.20	$254.20
Purchase #3	$57.56	8.153%	$62.2529	$62.25	$62.25	$62.30
Purchase #4	$207.89	6.690%	$221.7978	$221.80	$221.80	$221.80
Purchase #5	$38.93	11.451%	$43.3879	$43.39	$43.40	$43.40
Purchase #6	$47.85	9.191%	$52.2479	$52.25	$52.25	$52.20
Purchase #7	$142.92	11.523%	$159.3887	$159.39	$159.40	$159.40
7 purchase totals =	$755.24		$830.4049	$830.41	$830.40	$830.40