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	$134.54	11.496%	$150.0067	$150.01	$150.00	$150.00
Purchase #2	$26.47	6.470%	$28.1826	$28.18	$28.20	$28.20
Purchase #3	$76.89	7.448%	$82.6168	$82.62	$82.60	$82.60
Purchase #4	$45.45	10.263%	$50.1145	$50.11	$50.10	$50.10
Purchase #5	$116.29	6.470%	$123.814	$123.81	$123.80	$123.80
Purchase #6	$250.35	5.806%	$264.8853	$264.89	$264.90	$264.90
Purchase #7	$79.64	4.841%	$83.4954	$83.50	$83.50	$83.50
7 purchase totals =	$729.63		$783.1153	$783.12	$783.10	$783.10