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	$18.71	7.799%	$20.1692	$20.17	$20.15	$20.20
Purchase #2	$76.85	7.557%	$82.6576	$82.66	$82.65	$82.70
Purchase #3	$200.34	9.639%	$219.6508	$219.65	$219.65	$219.70
Purchase #4	$246.81	10.591%	$272.9496	$272.95	$272.95	$272.90
Purchase #5	$231.97	4.275%	$241.8867	$241.89	$241.90	$241.90
Purchase #6	$146.76	3.260%	$151.5444	$151.54	$151.55	$151.50
Purchase #7	$162.98	13.505%	$184.9904	$184.99	$185.00	$185.00
7 purchase totals =	$1,084.42		$1,173.8487	$1,173.85	$1,173.85	$1,173.90