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	$247.77	7.157%	$265.5029	$265.50	$265.50	$265.50
Purchase #2	$222.92	11.418%	$248.373	$248.37	$248.35	$248.40
Purchase #3	$124.31	13.273%	$140.8097	$140.81	$140.80	$140.80
Purchase #4	$178.34	10.390%	$196.8695	$196.87	$196.85	$196.90
Purchase #5	$127.71	11.717%	$142.6738	$142.67	$142.65	$142.70
Purchase #6	$119.61	11.363%	$133.2013	$133.20	$133.20	$133.20
Purchase #7	$56.30	9.378%	$61.5798	$61.58	$61.60	$61.60
7 purchase totals =	$1,076.96		$1,189.0100	$1,189.00	$1,188.95	$1,189.10