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	$29.35	6.200%	$31.1697	$31.17	$31.15	$31.20
Purchase #2	$61.88	9.425%	$67.7122	$67.71	$67.70	$67.70
Purchase #3	$61.42	4.694%	$64.3031	$64.30	$64.30	$64.30
Purchase #4	$169.61	11.126%	$188.4808	$188.48	$188.50	$188.50
Purchase #5	$164.53	3.144%	$169.7028	$169.70	$169.70	$169.70
Purchase #6	$106.47	4.658%	$111.4294	$111.43	$111.45	$111.40
Purchase #7	$151.64	11.679%	$169.35	$169.35	$169.35	$169.40
7 purchase totals =	$744.90		$802.1480	$802.14	$802.15	$802.20