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	$129.55	6.813%	$138.3762	$138.38	$138.40	$138.40
Purchase #2	$40.88	6.243%	$43.4321	$43.43	$43.45	$43.40
Purchase #3	$158.85	6.204%	$168.7051	$168.71	$168.70	$168.70
Purchase #4	$58.89	11.848%	$65.8673	$65.87	$65.85	$65.90
Purchase #5	$249.33	4.733%	$261.1308	$261.13	$261.15	$261.10
Purchase #6	$131.50	8.666%	$142.8958	$142.90	$142.90	$142.90
Purchase #7	$211.37	6.505%	$225.1196	$225.12	$225.10	$225.10
7 purchase totals =	$980.37		$1,045.5269	$1,045.54	$1,045.55	$1,045.50