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	$31.50	3.245%	$32.5222	$32.52	$32.50	$32.50
Purchase #2	$63.75	4.389%	$66.548	$66.55	$66.55	$66.50
Purchase #3	$215.39	3.178%	$222.2351	$222.24	$222.25	$222.20
Purchase #4	$128.70	9.844%	$141.3692	$141.37	$141.35	$141.40
Purchase #5	$135.72	4.123%	$141.3157	$141.32	$141.30	$141.30
Purchase #6	$41.39	5.202%	$43.5431	$43.54	$43.55	$43.50
Purchase #7	$24.45	8.320%	$26.4842	$26.48	$26.50	$26.50
7 purchase totals =	$640.90		$674.0175	$674.02	$674.00	$673.90