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	$75.36	13.506%	$85.5381	$85.54	$85.55	$85.50
Purchase #2	$132.69	13.833%	$151.045	$151.05	$151.05	$151.00
Purchase #3	$206.61	6.228%	$219.4777	$219.48	$219.50	$219.50
Purchase #4	$60.90	9.133%	$66.462	$66.46	$66.45	$66.50
Purchase #5	$28.29	8.206%	$30.6115	$30.61	$30.60	$30.60
Purchase #6	$35.87	13.575%	$40.7394	$40.74	$40.75	$40.70
Purchase #7	$241.31	5.673%	$254.9995	$255.00	$255.00	$255.00
7 purchase totals =	$781.03		$848.8732	$848.88	$848.90	$848.80