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	$9.26	13.445%	$10.505	$10.51	$10.50	$10.50
Purchase #2	$155.86	7.582%	$167.6773	$167.68	$167.70	$167.70
Purchase #3	$82.88	3.161%	$85.4998	$85.50	$85.50	$85.50
Purchase #4	$145.44	13.290%	$164.769	$164.77	$164.75	$164.80
Purchase #5	$150.83	9.483%	$165.1332	$165.13	$165.15	$165.10
Purchase #6	$140.31	6.688%	$149.6939	$149.69	$149.70	$149.70
Purchase #7	$29.96	9.341%	$32.7586	$32.76	$32.75	$32.80
7 purchase totals =	$714.54		$776.0368	$776.04	$776.05	$776.10