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	$36.30	4.551%	$37.952	$37.95	$37.95	$38.00
Purchase #2	$127.86	13.541%	$145.1735	$145.17	$145.15	$145.20
Purchase #3	$167.62	13.644%	$190.4901	$190.49	$190.50	$190.50
Purchase #4	$90.62	8.548%	$98.3662	$98.37	$98.35	$98.40
Purchase #5	$84.77	7.191%	$90.8658	$90.87	$90.85	$90.90
Purchase #6	$19.99	3.566%	$20.7028	$20.70	$20.70	$20.70
Purchase #7	$247.58	7.254%	$265.5395	$265.54	$265.55	$265.50
7 purchase totals =	$774.74		$849.0899	$849.09	$849.05	$849.20