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	$137.96	10.370%	$152.2665	$152.27	$152.25	$152.30
Purchase #2	$37.90	6.529%	$40.3745	$40.37	$40.35	$40.40
Purchase #3	$120.27	6.217%	$127.7472	$127.75	$127.75	$127.70
Purchase #4	$48.39	10.651%	$53.544	$53.54	$53.55	$53.50
Purchase #5	$84.52	5.125%	$88.8517	$88.85	$88.85	$88.90
Purchase #6	$203.47	11.605%	$227.0827	$227.08	$227.10	$227.10
Purchase #7	$199.67	13.431%	$226.4877	$226.49	$226.50	$226.50
7 purchase totals =	$832.18		$916.3543	$916.35	$916.35	$916.40