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	$20.51	6.371%	$21.8167	$21.82	$21.80	$21.80
Purchase #2	$140.78	5.370%	$148.3399	$148.34	$148.35	$148.30
Purchase #3	$68.59	12.446%	$77.1267	$77.13	$77.15	$77.10
Purchase #4	$129.37	13.220%	$146.4727	$146.47	$146.45	$146.50
Purchase #5	$95.55	11.647%	$106.6787	$106.68	$106.70	$106.70
Purchase #6	$189.51	3.639%	$196.4063	$196.41	$196.40	$196.40
Purchase #7	$152.41	9.394%	$166.7274	$166.73	$166.75	$166.70
7 purchase totals =	$796.72		$863.5684	$863.58	$863.60	$863.50