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	$37.33	13.745%	$42.461	$42.46	$42.45	$42.50
Purchase #2	$165.67	8.388%	$179.5664	$179.57	$179.55	$179.60
Purchase #3	$152.80	12.412%	$171.7655	$171.77	$171.75	$171.80
Purchase #4	$52.99	13.774%	$60.2888	$60.29	$60.30	$60.30
Purchase #5	$95.33	11.669%	$106.4541	$106.45	$106.45	$106.50
Purchase #6	$134.95	7.521%	$145.0996	$145.10	$145.10	$145.10
Purchase #7	$97.74	10.816%	$108.3116	$108.31	$108.30	$108.30
7 purchase totals =	$736.81		$813.9470	$813.95	$813.90	$814.10