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	$39.33	10.410%	$43.4243	$43.42	$43.40	$43.40
Purchase #2	$111.96	5.473%	$118.0876	$118.09	$118.10	$118.10
Purchase #3	$35.94	7.867%	$38.7674	$38.77	$38.75	$38.80
Purchase #4	$39.47	13.833%	$44.9299	$44.93	$44.95	$44.90
Purchase #5	$223.62	13.411%	$253.6097	$253.61	$253.60	$253.60
Purchase #6	$119.94	6.540%	$127.7841	$127.78	$127.80	$127.80
Purchase #7	$40.80	4.533%	$42.6495	$42.65	$42.65	$42.60
7 purchase totals =	$611.06		$669.2525	$669.25	$669.25	$669.20