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	$249.80	3.141%	$257.6462	$257.65	$257.65	$257.60
Purchase #2	$132.61	3.815%	$137.6691	$137.67	$137.65	$137.70
Purchase #3	$157.33	10.518%	$173.878	$173.88	$173.90	$173.90
Purchase #4	$180.39	8.330%	$195.4165	$195.42	$195.40	$195.40
Purchase #5	$38.52	10.519%	$42.5719	$42.57	$42.55	$42.60
Purchase #6	$41.73	8.778%	$45.3931	$45.39	$45.40	$45.40
Purchase #7	$38.63	9.162%	$42.1693	$42.17	$42.15	$42.20
7 purchase totals =	$839.01		$894.7441	$894.75	$894.70	$894.80