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	$28.29	13.732%	$32.1748	$32.17	$32.15	$32.20
Purchase #2	$225.73	6.330%	$240.0187	$240.02	$240.00	$240.00
Purchase #3	$228.68	11.734%	$255.5133	$255.51	$255.50	$255.50
Purchase #4	$135.33	3.614%	$140.2208	$140.22	$140.20	$140.20
Purchase #5	$49.80	11.510%	$55.532	$55.53	$55.55	$55.50
Purchase #6	$248.65	12.262%	$279.1395	$279.14	$279.15	$279.10
Purchase #7	$208.77	7.781%	$225.0144	$225.01	$225.00	$225.00
7 purchase totals =	$1,125.25		$1,227.6135	$1,227.60	$1,227.55	$1,227.50