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	$7.60	9.205%	$8.2996	$8.30	$8.30	$8.30
Purchase #2	$119.91	8.459%	$130.0532	$130.05	$130.05	$130.10
Purchase #3	$44.91	7.716%	$48.3753	$48.38	$48.40	$48.40
Purchase #4	$123.92	10.243%	$136.6131	$136.61	$136.60	$136.60
Purchase #5	$38.81	12.308%	$43.5867	$43.59	$43.60	$43.60
Purchase #6	$78.54	5.508%	$82.866	$82.87	$82.85	$82.90
Purchase #7	$150.49	5.611%	$158.934	$158.93	$158.95	$158.90
7 purchase totals =	$564.18		$608.7279	$608.73	$608.75	$608.80