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	$242.81	5.439%	$256.0164	$256.02	$256.00	$256.00
Purchase #2	$95.85	3.859%	$99.5489	$99.55	$99.55	$99.50
Purchase #3	$155.43	9.252%	$169.8104	$169.81	$169.80	$169.80
Purchase #4	$205.49	3.678%	$213.0479	$213.05	$213.05	$213.00
Purchase #5	$122.70	4.132%	$127.77	$127.77	$127.75	$127.80
Purchase #6	$83.78	8.388%	$90.8075	$90.81	$90.80	$90.80
Purchase #7	$33.47	12.115%	$37.5249	$37.52	$37.50	$37.50
7 purchase totals =	$939.53		$994.5260	$994.53	$994.45	$994.40