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	$61.45	12.526%	$69.1472	$69.15	$69.15	$69.10
Purchase #2	$79.74	13.498%	$90.5033	$90.50	$90.50	$90.50
Purchase #3	$124.93	11.674%	$139.5143	$139.51	$139.50	$139.50
Purchase #4	$149.59	12.421%	$168.1706	$168.17	$168.15	$168.20
Purchase #5	$219.91	9.687%	$241.2127	$241.21	$241.20	$241.20
Purchase #6	$37.83	10.291%	$41.7231	$41.72	$41.70	$41.70
Purchase #7	$15.53	5.184%	$16.3351	$16.34	$16.35	$16.30
7 purchase totals =	$688.98		$766.6063	$766.60	$766.55	$766.50