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	$141.81	12.242%	$159.1704	$159.17	$159.15	$159.20
Purchase #2	$112.34	11.384%	$125.1288	$125.13	$125.15	$125.10
Purchase #3	$80.78	10.452%	$89.2231	$89.22	$89.20	$89.20
Purchase #4	$141.81	10.513%	$156.7185	$156.72	$156.70	$156.70
Purchase #5	$57.73	4.358%	$60.2459	$60.25	$60.25	$60.20
Purchase #6	$123.34	13.778%	$140.3338	$140.33	$140.35	$140.30
Purchase #7	$112.97	6.796%	$120.6474	$120.65	$120.65	$120.60
7 purchase totals =	$770.78		$851.4679	$851.47	$851.45	$851.30