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	$236.33	8.281%	$255.9005	$255.90	$255.90	$255.90
Purchase #2	$122.74	13.439%	$139.235	$139.24	$139.25	$139.20
Purchase #3	$183.31	8.214%	$198.3671	$198.37	$198.35	$198.40
Purchase #4	$42.43	9.238%	$46.3497	$46.35	$46.35	$46.30
Purchase #5	$134.71	6.508%	$143.4769	$143.48	$143.50	$143.50
Purchase #6	$68.46	4.363%	$71.4469	$71.45	$71.45	$71.40
Purchase #7	$36.34	9.781%	$39.8944	$39.89	$39.90	$39.90
7 purchase totals =	$824.32		$894.6705	$894.68	$894.70	$894.60