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	$181.86	3.813%	$188.7943	$188.79	$188.80	$188.80
Purchase #2	$36.71	5.157%	$38.6031	$38.60	$38.60	$38.60
Purchase #3	$105.62	13.513%	$119.8924	$119.89	$119.90	$119.90
Purchase #4	$42.65	6.658%	$45.4896	$45.49	$45.50	$45.50
Purchase #5	$7.84	13.558%	$8.9029	$8.90	$8.90	$8.90
Purchase #6	$149.57	4.171%	$155.8086	$155.81	$155.80	$155.80
Purchase #7	$13.42	11.749%	$14.9967	$15.00	$15.00	$15.00
7 purchase totals =	$537.67		$572.4876	$572.48	$572.50	$572.50