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	$78.49	13.862%	$89.3703	$89.37	$89.35	$89.40
Purchase #2	$21.85	3.129%	$22.5337	$22.53	$22.55	$22.50
Purchase #3	$66.41	7.593%	$71.4525	$71.45	$71.45	$71.50
Purchase #4	$110.98	9.291%	$121.2912	$121.29	$121.30	$121.30
Purchase #5	$17.51	3.307%	$18.0891	$18.09	$18.10	$18.10
Purchase #6	$164.77	9.710%	$180.7692	$180.77	$180.75	$180.80
Purchase #7	$90.53	12.135%	$101.5158	$101.52	$101.50	$101.50
7 purchase totals =	$550.54		$605.0218	$605.02	$605.00	$605.10