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	$136.59	7.204%	$146.4299	$146.43	$146.45	$146.40
Purchase #2	$124.84	11.566%	$139.279	$139.28	$139.30	$139.30
Purchase #3	$21.33	13.309%	$24.1688	$24.17	$24.15	$24.20
Purchase #4	$140.39	4.436%	$146.6177	$146.62	$146.60	$146.60
Purchase #5	$51.77	4.578%	$54.14	$54.14	$54.15	$54.10
Purchase #6	$36.66	4.732%	$38.3948	$38.39	$38.40	$38.40
Purchase #7	$226.84	12.116%	$254.3239	$254.32	$254.30	$254.30
7 purchase totals =	$738.42		$803.3541	$803.35	$803.35	$803.30