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	$40.57	5.594%	$42.8395	$42.84	$42.85	$42.80
Purchase #2	$223.85	9.353%	$244.7867	$244.79	$244.80	$244.80
Purchase #3	$17.41	11.314%	$19.3798	$19.38	$19.40	$19.40
Purchase #4	$36.46	7.537%	$39.208	$39.21	$39.20	$39.20
Purchase #5	$114.86	3.179%	$118.5114	$118.51	$118.50	$118.50
Purchase #6	$82.28	4.259%	$85.7843	$85.78	$85.80	$85.80
Purchase #7	$245.58	12.486%	$276.2431	$276.24	$276.25	$276.20
7 purchase totals =	$761.01		$826.7528	$826.75	$826.80	$826.70