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	$30.64	6.758%	$32.7107	$32.71	$32.70	$32.70
Purchase #2	$43.53	5.203%	$45.7949	$45.79	$45.80	$45.80
Purchase #3	$186.61	3.777%	$193.6583	$193.66	$193.65	$193.70
Purchase #4	$82.77	8.134%	$89.5025	$89.50	$89.50	$89.50
Purchase #5	$133.61	4.149%	$139.1535	$139.15	$139.15	$139.20
Purchase #6	$159.56	9.743%	$175.1059	$175.11	$175.10	$175.10
Purchase #7	$218.89	3.479%	$226.5052	$226.51	$226.50	$226.50
7 purchase totals =	$855.61		$902.4310	$902.43	$902.40	$902.50