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	$86.87	4.460%	$90.7444	$90.74	$90.75	$90.70
Purchase #2	$36.89	12.707%	$41.5776	$41.58	$41.60	$41.60
Purchase #3	$147.73	12.722%	$166.5242	$166.52	$166.50	$166.50
Purchase #4	$17.79	6.700%	$18.9819	$18.98	$19.00	$19.00
Purchase #5	$123.45	4.277%	$128.73	$128.73	$128.75	$128.70
Purchase #6	$31.30	6.193%	$33.2384	$33.24	$33.25	$33.20
Purchase #7	$209.56	10.291%	$231.1258	$231.13	$231.15	$231.10
7 purchase totals =	$653.59		$710.9223	$710.92	$711.00	$710.80