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	$36.51	11.763%	$40.8047	$40.80	$40.80	$40.80
Purchase #2	$106.88	6.386%	$113.7054	$113.71	$113.70	$113.70
Purchase #3	$141.29	6.495%	$150.4668	$150.47	$150.45	$150.50
Purchase #4	$55.39	8.727%	$60.2239	$60.22	$60.20	$60.20
Purchase #5	$14.71	12.350%	$16.5267	$16.53	$16.55	$16.50
Purchase #6	$199.30	4.813%	$208.8923	$208.89	$208.90	$208.90
Purchase #7	$54.78	8.850%	$59.628	$59.63	$59.65	$59.60
7 purchase totals =	$608.86		$650.2478	$650.25	$650.25	$650.20