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	$227.53	12.118%	$255.1021	$255.10	$255.10	$255.10
Purchase #2	$173.79	9.653%	$190.5659	$190.57	$190.55	$190.60
Purchase #3	$66.94	4.816%	$70.1638	$70.16	$70.15	$70.20
Purchase #4	$142.26	4.630%	$148.8466	$148.85	$148.85	$148.80
Purchase #5	$215.77	3.726%	$223.8096	$223.81	$223.80	$223.80
Purchase #6	$59.70	3.683%	$61.8988	$61.90	$61.90	$61.90
Purchase #7	$118.39	10.239%	$130.512	$130.51	$130.50	$130.50
7 purchase totals =	$1,004.38		$1,080.8988	$1,080.90	$1,080.85	$1,080.90