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	$39.37	3.520%	$40.7558	$40.76	$40.75	$40.80
Purchase #2	$40.77	6.589%	$43.4563	$43.46	$43.45	$43.50
Purchase #3	$100.51	8.185%	$108.7367	$108.74	$108.75	$108.70
Purchase #4	$28.48	12.496%	$32.0389	$32.04	$32.05	$32.00
Purchase #5	$26.68	12.763%	$30.0852	$30.09	$30.10	$30.10
Purchase #6	$134.96	11.285%	$150.1902	$150.19	$150.20	$150.20
Purchase #7	$35.69	13.455%	$40.4921	$40.49	$40.50	$40.50
7 purchase totals =	$406.46		$445.7552	$445.77	$445.80	$445.80