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	$89.52	4.165%	$93.2485	$93.25	$93.25	$93.20
Purchase #2	$239.43	9.592%	$262.3961	$262.40	$262.40	$262.40
Purchase #3	$144.27	7.355%	$154.8811	$154.88	$154.90	$154.90
Purchase #4	$18.77	11.608%	$20.9488	$20.95	$20.95	$20.90
Purchase #5	$133.98	11.433%	$149.2979	$149.30	$149.30	$149.30
Purchase #6	$124.42	4.773%	$130.3586	$130.36	$130.35	$130.40
Purchase #7	$83.99	6.167%	$89.1697	$89.17	$89.15	$89.20
7 purchase totals =	$834.38		$900.3007	$900.31	$900.30	$900.30