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	$128.47	3.636%	$133.1412	$133.14	$133.15	$133.10
Purchase #2	$66.85	6.516%	$71.2059	$71.21	$71.20	$71.20
Purchase #3	$30.46	11.252%	$33.8874	$33.89	$33.90	$33.90
Purchase #4	$175.73	5.778%	$185.8837	$185.88	$185.90	$185.90
Purchase #5	$176.37	8.237%	$190.8976	$190.90	$190.90	$190.90
Purchase #6	$137.63	6.742%	$146.909	$146.91	$146.90	$146.90
Purchase #7	$47.95	13.558%	$54.4511	$54.45	$54.45	$54.50
7 purchase totals =	$763.46		$816.3759	$816.38	$816.40	$816.40