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	$75.48	3.515%	$78.1331	$78.13	$78.15	$78.10
Purchase #2	$220.53	5.479%	$232.6128	$232.61	$232.60	$232.60
Purchase #3	$203.61	9.703%	$223.3663	$223.37	$223.35	$223.40
Purchase #4	$99.71	11.770%	$111.4459	$111.45	$111.45	$111.40
Purchase #5	$31.58	9.624%	$34.6193	$34.62	$34.60	$34.60
Purchase #6	$211.85	5.599%	$223.7115	$223.71	$223.70	$223.70
Purchase #7	$37.82	11.720%	$42.2525	$42.25	$42.25	$42.30
7 purchase totals =	$880.58		$946.1414	$946.14	$946.10	$946.10