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	$150.33	12.343%	$168.8852	$168.89	$168.90	$168.90
Purchase #2	$247.80	7.302%	$265.8944	$265.89	$265.90	$265.90
Purchase #3	$210.90	11.778%	$235.7398	$235.74	$235.75	$235.70
Purchase #4	$202.94	10.837%	$224.9326	$224.93	$224.95	$224.90
Purchase #5	$212.68	9.768%	$233.4546	$233.45	$233.45	$233.50
Purchase #6	$212.79	4.843%	$223.0954	$223.10	$223.10	$223.10
Purchase #7	$88.49	12.428%	$99.4875	$99.49	$99.50	$99.50
7 purchase totals =	$1,325.93		$1,451.4895	$1,451.49	$1,451.55	$1,451.50