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	$119.31	3.507%	$123.4942	$123.49	$123.50	$123.50
Purchase #2	$50.70	7.732%	$54.6201	$54.62	$54.60	$54.60
Purchase #3	$63.61	12.147%	$71.3367	$71.34	$71.35	$71.30
Purchase #4	$87.54	11.231%	$97.3716	$97.37	$97.35	$97.40
Purchase #5	$44.34	3.319%	$45.8116	$45.81	$45.80	$45.80
Purchase #6	$48.45	9.721%	$53.1598	$53.16	$53.15	$53.20
Purchase #7	$155.57	10.428%	$171.7928	$171.79	$171.80	$171.80
7 purchase totals =	$569.52		$617.5868	$617.58	$617.55	$617.60