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	$172.78	6.329%	$183.7152	$183.72	$183.70	$183.70
Purchase #2	$234.68	8.172%	$253.858	$253.86	$253.85	$253.90
Purchase #3	$100.74	7.796%	$108.5937	$108.59	$108.60	$108.60
Purchase #4	$33.70	4.495%	$35.2148	$35.21	$35.20	$35.20
Purchase #5	$24.77	3.844%	$25.7222	$25.72	$25.70	$25.70
Purchase #6	$91.73	11.836%	$102.5872	$102.59	$102.60	$102.60
Purchase #7	$85.30	5.136%	$89.681	$89.68	$89.70	$89.70
7 purchase totals =	$743.70		$799.3721	$799.37	$799.35	$799.40