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	$76.50	4.357%	$79.8331	$79.83	$79.85	$79.80
Purchase #2	$120.95	8.740%	$131.521	$131.52	$131.50	$131.50
Purchase #3	$13.43	13.595%	$15.2558	$15.26	$15.25	$15.30
Purchase #4	$132.70	6.107%	$140.804	$140.80	$140.80	$140.80
Purchase #5	$6.56	13.791%	$7.4647	$7.46	$7.45	$7.50
Purchase #6	$40.56	11.491%	$45.2207	$45.22	$45.20	$45.20
Purchase #7	$92.61	13.517%	$105.1281	$105.13	$105.15	$105.10
7 purchase totals =	$483.31		$525.2274	$525.22	$525.20	$525.20