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	$56.71	5.478%	$59.8166	$59.82	$59.80	$59.80
Purchase #2	$227.39	13.784%	$258.7334	$258.73	$258.75	$258.70
Purchase #3	$126.72	11.108%	$140.7961	$140.80	$140.80	$140.80
Purchase #4	$25.69	3.645%	$26.6264	$26.63	$26.65	$26.60
Purchase #5	$141.59	4.323%	$147.7109	$147.71	$147.70	$147.70
Purchase #6	$87.63	3.370%	$90.5831	$90.58	$90.60	$90.60
Purchase #7	$104.34	11.226%	$116.0532	$116.05	$116.05	$116.10
7 purchase totals =	$770.07		$840.3197	$840.32	$840.35	$840.30