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	$31.27	3.574%	$32.3876	$32.39	$32.40	$32.40
Purchase #2	$212.65	4.218%	$221.6196	$221.62	$221.60	$221.60
Purchase #3	$133.56	7.700%	$143.8441	$143.84	$143.85	$143.80
Purchase #4	$106.89	7.711%	$115.1323	$115.13	$115.15	$115.10
Purchase #5	$83.58	3.759%	$86.7218	$86.72	$86.70	$86.70
Purchase #6	$151.43	13.695%	$172.1683	$172.17	$172.15	$172.20
Purchase #7	$225.59	3.316%	$233.0706	$233.07	$233.05	$233.10
7 purchase totals =	$944.97		$1,004.9443	$1,004.94	$1,004.90	$1,004.90