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	$53.44	10.295%	$58.9416	$58.94	$58.95	$58.90
Purchase #2	$216.75	13.730%	$246.5098	$246.51	$246.50	$246.50
Purchase #3	$189.33	3.546%	$196.0436	$196.04	$196.05	$196.00
Purchase #4	$36.78	10.676%	$40.7066	$40.71	$40.70	$40.70
Purchase #5	$127.97	10.196%	$141.0178	$141.02	$141.00	$141.00
Purchase #6	$105.76	5.214%	$111.2743	$111.27	$111.25	$111.30
Purchase #7	$184.58	7.257%	$197.975	$197.98	$198.00	$198.00
7 purchase totals =	$914.61		$992.4687	$992.47	$992.45	$992.40