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	$80.69	11.379%	$89.8717	$89.87	$89.85	$89.90
Purchase #2	$64.36	11.735%	$71.9126	$71.91	$71.90	$71.90
Purchase #3	$236.69	11.687%	$264.352	$264.35	$264.35	$264.40
Purchase #4	$179.85	4.316%	$187.6123	$187.61	$187.60	$187.60
Purchase #5	$40.78	9.576%	$44.6851	$44.69	$44.70	$44.70
Purchase #6	$146.80	9.838%	$161.2422	$161.24	$161.25	$161.20
Purchase #7	$143.43	3.658%	$148.6767	$148.68	$148.70	$148.70
7 purchase totals =	$892.60		$968.3526	$968.35	$968.35	$968.40