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	$99.39	13.109%	$112.419	$112.42	$112.40	$112.40
Purchase #2	$202.93	10.266%	$223.7628	$223.76	$223.75	$223.80
Purchase #3	$227.79	6.136%	$241.7672	$241.77	$241.75	$241.80
Purchase #4	$86.74	9.702%	$95.1555	$95.16	$95.15	$95.20
Purchase #5	$143.57	8.330%	$155.5294	$155.53	$155.55	$155.50
Purchase #6	$29.25	12.766%	$32.9841	$32.98	$33.00	$33.00
Purchase #7	$67.83	8.847%	$73.8309	$73.83	$73.85	$73.80
7 purchase totals =	$857.50		$935.4489	$935.45	$935.45	$935.50