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	$140.37	12.802%	$158.3402	$158.34	$158.35	$158.30
Purchase #2	$171.77	10.698%	$190.146	$190.15	$190.15	$190.10
Purchase #3	$144.76	8.830%	$157.5423	$157.54	$157.55	$157.50
Purchase #4	$69.50	3.221%	$71.7386	$71.74	$71.75	$71.70
Purchase #5	$136.39	11.713%	$152.3654	$152.37	$152.35	$152.40
Purchase #6	$10.37	6.127%	$11.0054	$11.01	$11.00	$11.00
Purchase #7	$176.66	4.543%	$184.6857	$184.69	$184.70	$184.70
7 purchase totals =	$849.82		$925.8236	$925.84	$925.85	$925.70