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	$95.78	7.421%	$102.8878	$102.89	$102.90	$102.90
Purchase #2	$136.96	7.244%	$146.8814	$146.88	$146.90	$146.90
Purchase #3	$41.85	8.569%	$45.4361	$45.44	$45.45	$45.40
Purchase #4	$57.94	5.733%	$61.2617	$61.26	$61.25	$61.30
Purchase #5	$55.80	7.439%	$59.951	$59.95	$59.95	$60.00
Purchase #6	$113.31	11.491%	$126.3305	$126.33	$126.35	$126.30
Purchase #7	$125.34	5.263%	$131.9366	$131.94	$131.95	$131.90
7 purchase totals =	$626.98		$674.6851	$674.69	$674.75	$674.70