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	$57.26	9.173%	$62.5125	$62.51	$62.50	$62.50
Purchase #2	$64.89	10.729%	$71.852	$71.85	$71.85	$71.90
Purchase #3	$123.71	12.770%	$139.5078	$139.51	$139.50	$139.50
Purchase #4	$123.74	3.192%	$127.6898	$127.69	$127.70	$127.70
Purchase #5	$120.50	7.593%	$129.6496	$129.65	$129.65	$129.60
Purchase #6	$44.77	6.648%	$47.7463	$47.75	$47.75	$47.70
Purchase #7	$59.41	8.679%	$64.5662	$64.57	$64.55	$64.60
7 purchase totals =	$594.28		$643.5242	$643.53	$643.50	$643.50