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	$44.68	6.504%	$47.586	$47.59	$47.60	$47.60
Purchase #2	$135.73	3.779%	$140.8592	$140.86	$140.85	$140.90
Purchase #3	$136.58	11.518%	$152.3113	$152.31	$152.30	$152.30
Purchase #4	$97.36	13.221%	$110.232	$110.23	$110.25	$110.20
Purchase #5	$37.58	7.342%	$40.3391	$40.34	$40.35	$40.30
Purchase #6	$56.73	4.377%	$59.2131	$59.21	$59.20	$59.20
Purchase #7	$121.73	5.502%	$128.4276	$128.43	$128.45	$128.40
7 purchase totals =	$630.39		$678.9683	$678.97	$679.00	$678.90