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	$89.44	12.688%	$100.7881	$100.79	$100.80	$100.80
Purchase #2	$62.31	6.615%	$66.4318	$66.43	$66.45	$66.40
Purchase #3	$37.59	11.352%	$41.8572	$41.86	$41.85	$41.90
Purchase #4	$16.66	8.684%	$18.1068	$18.11	$18.10	$18.10
Purchase #5	$176.77	7.613%	$190.2275	$190.23	$190.25	$190.20
Purchase #6	$32.74	7.220%	$35.1038	$35.10	$35.10	$35.10
Purchase #7	$49.26	10.729%	$54.5451	$54.55	$54.55	$54.50
7 purchase totals =	$464.77		$507.0603	$507.07	$507.10	$507.00