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	$73.44	6.244%	$78.0256	$78.03	$78.05	$78.00
Purchase #2	$85.33	11.581%	$95.2121	$95.21	$95.20	$95.20
Purchase #3	$96.49	9.733%	$105.8814	$105.88	$105.90	$105.90
Purchase #4	$160.42	4.743%	$168.0287	$168.03	$168.05	$168.00
Purchase #5	$87.82	9.142%	$95.8485	$95.85	$95.85	$95.80
Purchase #6	$85.61	4.511%	$89.4719	$89.47	$89.45	$89.50
Purchase #7	$245.98	3.244%	$253.9596	$253.96	$253.95	$254.00
7 purchase totals =	$835.09		$886.4278	$886.43	$886.45	$886.40