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	$11.86	12.292%	$13.3178	$13.32	$13.30	$13.30
Purchase #2	$122.55	7.260%	$131.4471	$131.45	$131.45	$131.40
Purchase #3	$40.89	10.424%	$45.1524	$45.15	$45.15	$45.20
Purchase #4	$212.82	8.421%	$230.7416	$230.74	$230.75	$230.70
Purchase #5	$25.32	5.379%	$26.682	$26.68	$26.70	$26.70
Purchase #6	$34.78	8.119%	$37.6038	$37.60	$37.60	$37.60
Purchase #7	$59.64	3.397%	$61.666	$61.67	$61.65	$61.70
7 purchase totals =	$507.86		$546.6107	$546.61	$546.60	$546.60