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	$46.59	4.290%	$48.5887	$48.59	$48.60	$48.60
Purchase #2	$213.77	7.439%	$229.6724	$229.67	$229.65	$229.70
Purchase #3	$149.58	9.307%	$163.5014	$163.50	$163.50	$163.50
Purchase #4	$141.55	12.661%	$159.4716	$159.47	$159.45	$159.50
Purchase #5	$150.48	3.481%	$155.7182	$155.72	$155.70	$155.70
Purchase #6	$39.54	6.579%	$42.1413	$42.14	$42.15	$42.10
Purchase #7	$198.82	10.384%	$219.4655	$219.47	$219.45	$219.50
7 purchase totals =	$940.33		$1,018.5591	$1,018.56	$1,018.50	$1,018.60