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	$130.32	12.115%	$146.1083	$146.11	$146.10	$146.10
Purchase #2	$36.54	11.324%	$40.6778	$40.68	$40.70	$40.70
Purchase #3	$100.60	7.783%	$108.4297	$108.43	$108.45	$108.40
Purchase #4	$24.86	11.657%	$27.7579	$27.76	$27.75	$27.80
Purchase #5	$123.48	9.851%	$135.644	$135.64	$135.65	$135.60
Purchase #6	$85.41	4.374%	$89.1458	$89.15	$89.15	$89.10
Purchase #7	$113.30	5.783%	$119.8521	$119.85	$119.85	$119.90
7 purchase totals =	$614.51		$667.6156	$667.62	$667.65	$667.60