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	$234.47	4.289%	$244.5264	$244.53	$244.55	$244.50
Purchase #2	$95.83	3.700%	$99.3757	$99.38	$99.40	$99.40
Purchase #3	$87.66	13.582%	$99.566	$99.57	$99.55	$99.60
Purchase #4	$95.78	9.797%	$105.1636	$105.16	$105.15	$105.20
Purchase #5	$15.71	12.517%	$17.6764	$17.68	$17.70	$17.70
Purchase #6	$173.74	6.666%	$185.3215	$185.32	$185.30	$185.30
Purchase #7	$111.42	13.302%	$126.2411	$126.24	$126.25	$126.20
7 purchase totals =	$814.61		$877.8707	$877.88	$877.90	$877.90