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	$35.55	10.702%	$39.3546	$39.35	$39.35	$39.40
Purchase #2	$71.34	4.137%	$74.2913	$74.29	$74.30	$74.30
Purchase #3	$211.54	5.781%	$223.7691	$223.77	$223.75	$223.80
Purchase #4	$184.69	12.833%	$208.3913	$208.39	$208.40	$208.40
Purchase #5	$54.51	9.615%	$59.7511	$59.75	$59.75	$59.80
Purchase #6	$152.45	10.335%	$168.2057	$168.21	$168.20	$168.20
Purchase #7	$131.44	4.606%	$137.4941	$137.49	$137.50	$137.50
7 purchase totals =	$841.52		$911.2572	$911.25	$911.25	$911.40