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	$51.56	7.755%	$55.5585	$55.56	$55.55	$55.60
Purchase #2	$126.63	4.177%	$131.9193	$131.92	$131.90	$131.90
Purchase #3	$137.38	12.770%	$154.9234	$154.92	$154.90	$154.90
Purchase #4	$249.72	11.800%	$279.187	$279.19	$279.20	$279.20
Purchase #5	$208.64	8.185%	$225.7172	$225.72	$225.70	$225.70
Purchase #6	$146.58	6.360%	$155.9025	$155.90	$155.90	$155.90
Purchase #7	$41.77	7.823%	$45.0377	$45.04	$45.05	$45.00
7 purchase totals =	$962.28		$1,048.2456	$1,048.25	$1,048.20	$1,048.20