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	$6.89	11.606%	$7.6897	$7.69	$7.70	$7.70
Purchase #2	$132.63	13.484%	$150.5138	$150.51	$150.50	$150.50
Purchase #3	$148.75	11.379%	$165.6763	$165.68	$165.70	$165.70
Purchase #4	$100.92	4.447%	$105.4079	$105.41	$105.40	$105.40
Purchase #5	$18.89	3.259%	$19.5056	$19.51	$19.50	$19.50
Purchase #6	$212.30	10.515%	$234.6233	$234.62	$234.60	$234.60
Purchase #7	$248.54	12.187%	$278.8296	$278.83	$278.85	$278.80
7 purchase totals =	$868.92		$962.2462	$962.25	$962.25	$962.20