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	$221.46	13.653%	$251.6959	$251.70	$251.70	$251.70
Purchase #2	$122.82	4.122%	$127.8826	$127.88	$127.90	$127.90
Purchase #3	$49.51	10.382%	$54.6501	$54.65	$54.65	$54.70
Purchase #4	$162.90	4.649%	$170.4732	$170.47	$170.45	$170.50
Purchase #5	$182.81	9.668%	$200.4841	$200.48	$200.50	$200.50
Purchase #6	$101.69	9.748%	$111.6027	$111.60	$111.60	$111.60
Purchase #7	$37.38	7.293%	$40.1061	$40.11	$40.10	$40.10
7 purchase totals =	$878.57		$956.8947	$956.89	$956.90	$957.00