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	$165.32	4.239%	$172.3279	$172.33	$172.35	$172.30
Purchase #2	$203.59	11.674%	$227.3571	$227.36	$227.35	$227.40
Purchase #3	$190.71	12.472%	$214.4954	$214.50	$214.50	$214.50
Purchase #4	$33.49	11.114%	$37.2121	$37.21	$37.20	$37.20
Purchase #5	$111.67	6.401%	$118.818	$118.82	$118.80	$118.80
Purchase #6	$84.30	5.160%	$88.6499	$88.65	$88.65	$88.60
Purchase #7	$69.47	12.394%	$78.0801	$78.08	$78.10	$78.10
7 purchase totals =	$858.55		$936.9405	$936.95	$936.95	$936.90