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	$187.33	6.445%	$199.4034	$199.40	$199.40	$199.40
Purchase #2	$86.50	9.189%	$94.4485	$94.45	$94.45	$94.40
Purchase #3	$89.72	11.704%	$100.2208	$100.22	$100.20	$100.20
Purchase #4	$64.58	10.322%	$71.2459	$71.25	$71.25	$71.20
Purchase #5	$51.55	11.499%	$57.4777	$57.48	$57.50	$57.50
Purchase #6	$118.26	12.492%	$133.033	$133.03	$133.05	$133.00
Purchase #7	$85.57	5.733%	$90.4757	$90.48	$90.50	$90.50
7 purchase totals =	$683.51		$746.3050	$746.31	$746.35	$746.20