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	$228.57	11.785%	$255.507	$255.51	$255.50	$255.50
Purchase #2	$190.70	4.197%	$198.7037	$198.70	$198.70	$198.70
Purchase #3	$113.30	5.352%	$119.3638	$119.36	$119.35	$119.40
Purchase #4	$92.57	7.205%	$99.2397	$99.24	$99.25	$99.20
Purchase #5	$211.46	9.581%	$231.72	$231.72	$231.70	$231.70
Purchase #6	$33.40	13.247%	$37.8245	$37.82	$37.80	$37.80
Purchase #7	$20.53	7.668%	$22.1042	$22.10	$22.10	$22.10
7 purchase totals =	$890.53		$964.4629	$964.45	$964.40	$964.40