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	$200.57	13.593%	$227.8335	$227.83	$227.85	$227.80
Purchase #2	$61.31	8.178%	$66.3239	$66.32	$66.30	$66.30
Purchase #3	$200.52	11.412%	$223.4033	$223.40	$223.40	$223.40
Purchase #4	$33.86	6.422%	$36.0345	$36.03	$36.05	$36.00
Purchase #5	$248.92	11.198%	$276.7941	$276.79	$276.80	$276.80
Purchase #6	$209.34	6.809%	$223.594	$223.59	$223.60	$223.60
Purchase #7	$215.77	11.197%	$239.9298	$239.93	$239.95	$239.90
7 purchase totals =	$1,170.29		$1,293.9131	$1,293.89	$1,293.95	$1,293.80