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	$15.91	11.145%	$17.6832	$17.68	$17.70	$17.70
Purchase #2	$111.91	12.203%	$125.5664	$125.57	$125.55	$125.60
Purchase #3	$104.48	7.528%	$112.3453	$112.35	$112.35	$112.30
Purchase #4	$76.96	12.500%	$86.58	$86.58	$86.60	$86.60
Purchase #5	$17.88	12.691%	$20.1492	$20.15	$20.15	$20.10
Purchase #6	$172.30	4.654%	$180.3188	$180.32	$180.30	$180.30
Purchase #7	$61.85	9.707%	$67.8538	$67.85	$67.85	$67.90
7 purchase totals =	$561.29		$610.4967	$610.50	$610.50	$610.50