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	$248.49	3.619%	$257.4829	$257.48	$257.50	$257.50
Purchase #2	$121.58	7.548%	$130.7569	$130.76	$130.75	$130.80
Purchase #3	$32.37	4.755%	$33.9092	$33.91	$33.90	$33.90
Purchase #4	$202.41	9.160%	$220.9508	$220.95	$220.95	$221.00
Purchase #5	$44.30	13.822%	$50.4231	$50.42	$50.40	$50.40
Purchase #6	$151.37	4.581%	$158.3043	$158.30	$158.30	$158.30
Purchase #7	$95.37	4.750%	$99.9001	$99.90	$99.90	$99.90
7 purchase totals =	$895.89		$951.7273	$951.72	$951.70	$951.80