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	$97.71	13.839%	$111.2321	$111.23	$111.25	$111.20
Purchase #2	$164.82	3.685%	$170.8936	$170.89	$170.90	$170.90
Purchase #3	$202.53	7.565%	$217.8514	$217.85	$217.85	$217.90
Purchase #4	$36.82	10.414%	$40.6544	$40.65	$40.65	$40.70
Purchase #5	$171.63	8.420%	$186.0812	$186.08	$186.10	$186.10
Purchase #6	$30.36	5.546%	$32.0438	$32.04	$32.05	$32.00
Purchase #7	$62.29	8.376%	$67.5074	$67.51	$67.50	$67.50
7 purchase totals =	$766.16		$826.2639	$826.25	$826.30	$826.30