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	$54.46	12.392%	$61.2087	$61.21	$61.20	$61.20
Purchase #2	$91.71	10.718%	$101.5395	$101.54	$101.55	$101.50
Purchase #3	$102.96	8.594%	$111.8084	$111.81	$111.80	$111.80
Purchase #4	$217.49	10.780%	$240.9354	$240.94	$240.95	$240.90
Purchase #5	$133.44	8.580%	$144.8892	$144.89	$144.90	$144.90
Purchase #6	$204.26	12.325%	$229.435	$229.44	$229.45	$229.40
Purchase #7	$136.65	10.313%	$150.7427	$150.74	$150.75	$150.70
7 purchase totals =	$940.97		$1,040.5589	$1,040.57	$1,040.60	$1,040.40