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	$52.82	13.130%	$59.7553	$59.76	$59.75	$59.80
Purchase #2	$142.25	12.807%	$160.468	$160.47	$160.45	$160.50
Purchase #3	$194.50	6.192%	$206.5434	$206.54	$206.55	$206.50
Purchase #4	$70.42	3.537%	$72.9108	$72.91	$72.90	$72.90
Purchase #5	$61.28	9.257%	$66.9527	$66.95	$66.95	$67.00
Purchase #6	$21.86	13.178%	$24.7407	$24.74	$24.75	$24.70
Purchase #7	$56.27	3.784%	$58.3993	$58.40	$58.40	$58.40
7 purchase totals =	$599.40		$649.7702	$649.77	$649.75	$649.80