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	$135.75	7.754%	$146.2761	$146.28	$146.30	$146.30
Purchase #2	$224.60	13.199%	$254.245	$254.25	$254.25	$254.20
Purchase #3	$50.46	7.318%	$54.1527	$54.15	$54.15	$54.20
Purchase #4	$61.96	9.158%	$67.6343	$67.63	$67.65	$67.60
Purchase #5	$109.39	13.199%	$123.8284	$123.83	$123.85	$123.80
Purchase #6	$150.44	13.522%	$170.7825	$170.78	$170.80	$170.80
Purchase #7	$51.40	6.588%	$54.7862	$54.79	$54.80	$54.80
7 purchase totals =	$784.00		$871.7052	$871.71	$871.80	$871.70