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	$135.53	11.856%	$151.5984	$151.60	$151.60	$151.60
Purchase #2	$231.46	7.740%	$249.375	$249.38	$249.40	$249.40
Purchase #3	$174.27	12.141%	$195.4281	$195.43	$195.45	$195.40
Purchase #4	$79.89	11.659%	$89.2044	$89.20	$89.20	$89.20
Purchase #5	$247.44	8.105%	$267.495	$267.50	$267.50	$267.50
Purchase #6	$89.82	11.438%	$100.0936	$100.09	$100.10	$100.10
Purchase #7	$31.54	8.348%	$34.173	$34.17	$34.15	$34.20
7 purchase totals =	$989.95		$1,087.3675	$1,087.37	$1,087.40	$1,087.40