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	$100.51	8.302%	$108.8543	$108.85	$108.85	$108.90
Purchase #2	$176.71	4.790%	$185.1744	$185.17	$185.15	$185.20
Purchase #3	$74.52	7.470%	$80.0866	$80.09	$80.10	$80.10
Purchase #4	$101.71	4.474%	$106.2605	$106.26	$106.25	$106.30
Purchase #5	$125.57	10.692%	$138.9959	$139.00	$139.00	$139.00
Purchase #6	$40.68	11.702%	$45.4404	$45.44	$45.45	$45.40
Purchase #7	$57.31	9.112%	$62.5321	$62.53	$62.55	$62.50
7 purchase totals =	$677.01		$727.3442	$727.34	$727.35	$727.40