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	$129.26	7.713%	$139.2298	$139.23	$139.25	$139.20
Purchase #2	$94.27	5.797%	$99.7348	$99.73	$99.75	$99.70
Purchase #3	$89.77	10.417%	$99.1213	$99.12	$99.10	$99.10
Purchase #4	$183.41	6.785%	$195.8544	$195.85	$195.85	$195.90
Purchase #5	$33.79	9.698%	$37.067	$37.07	$37.05	$37.10
Purchase #6	$44.70	3.833%	$46.4134	$46.41	$46.40	$46.40
Purchase #7	$223.89	3.818%	$232.4381	$232.44	$232.45	$232.40
7 purchase totals =	$799.09		$849.8588	$849.85	$849.85	$849.80