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	$109.74	8.844%	$119.4454	$119.45	$119.45	$119.40
Purchase #2	$95.46	5.695%	$100.8964	$100.90	$100.90	$100.90
Purchase #3	$199.76	13.726%	$227.1791	$227.18	$227.20	$227.20
Purchase #4	$138.63	11.485%	$154.5517	$154.55	$154.55	$154.60
Purchase #5	$28.56	12.186%	$32.0403	$32.04	$32.05	$32.00
Purchase #6	$115.97	10.494%	$128.1399	$128.14	$128.15	$128.10
Purchase #7	$65.64	9.537%	$71.9001	$71.90	$71.90	$71.90
7 purchase totals =	$753.76		$834.1529	$834.16	$834.20	$834.10