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	$139.31	10.123%	$153.4124	$153.41	$153.40	$153.40
Purchase #2	$125.89	6.539%	$134.1219	$134.12	$134.10	$134.10
Purchase #3	$148.62	11.362%	$165.5062	$165.51	$165.50	$165.50
Purchase #4	$247.32	11.240%	$275.1188	$275.12	$275.10	$275.10
Purchase #5	$76.43	3.513%	$79.115	$79.12	$79.10	$79.10
Purchase #6	$206.40	7.574%	$222.0327	$222.03	$222.05	$222.00
Purchase #7	$183.58	8.196%	$198.6262	$198.63	$198.65	$198.60
7 purchase totals =	$1,127.55		$1,227.9332	$1,227.94	$1,227.90	$1,227.80