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	$40.33	4.160%	$42.0077	$42.01	$42.00	$42.00
Purchase #2	$114.64	8.361%	$124.2251	$124.23	$124.25	$124.20
Purchase #3	$12.68	13.486%	$14.39	$14.39	$14.40	$14.40
Purchase #4	$75.83	12.604%	$85.3876	$85.39	$85.40	$85.40
Purchase #5	$190.31	5.496%	$200.7694	$200.77	$200.75	$200.80
Purchase #6	$141.91	8.293%	$153.6786	$153.68	$153.70	$153.70
Purchase #7	$18.81	12.539%	$21.1686	$21.17	$21.15	$21.20
7 purchase totals =	$594.51		$641.6270	$641.64	$641.65	$641.70