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	$92.36	13.358%	$104.6974	$104.70	$104.70	$104.70
Purchase #2	$108.82	9.148%	$118.7749	$118.77	$118.75	$118.80
Purchase #3	$60.38	11.760%	$67.4807	$67.48	$67.50	$67.50
Purchase #4	$250.94	9.795%	$275.5196	$275.52	$275.50	$275.50
Purchase #5	$77.27	9.222%	$84.3958	$84.40	$84.40	$84.40
Purchase #6	$196.69	4.384%	$205.3129	$205.31	$205.30	$205.30
Purchase #7	$107.91	7.731%	$116.2525	$116.25	$116.25	$116.30
7 purchase totals =	$894.37		$972.4338	$972.43	$972.40	$972.50