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	$89.35	6.588%	$95.2364	$95.24	$95.25	$95.20
Purchase #2	$242.32	13.298%	$274.5437	$274.54	$274.55	$274.50
Purchase #3	$76.54	4.594%	$80.0562	$80.06	$80.05	$80.10
Purchase #4	$42.44	6.761%	$45.3094	$45.31	$45.30	$45.30
Purchase #5	$59.79	11.348%	$66.575	$66.58	$66.60	$66.60
Purchase #6	$7.89	9.311%	$8.6246	$8.62	$8.60	$8.60
Purchase #7	$197.29	13.166%	$223.2652	$223.27	$223.25	$223.30
7 purchase totals =	$715.62		$793.6105	$793.62	$793.60	$793.60