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	$93.59	6.532%	$99.7033	$99.70	$99.70	$99.70
Purchase #2	$78.50	6.715%	$83.7713	$83.77	$83.75	$83.80
Purchase #3	$70.42	11.197%	$78.3049	$78.30	$78.30	$78.30
Purchase #4	$233.63	11.188%	$259.7685	$259.77	$259.75	$259.80
Purchase #5	$225.30	7.329%	$241.8122	$241.81	$241.80	$241.80
Purchase #6	$62.56	10.166%	$68.9198	$68.92	$68.90	$68.90
Purchase #7	$87.77	9.198%	$95.8431	$95.84	$95.85	$95.80
7 purchase totals =	$851.77		$928.1231	$928.11	$928.05	$928.10