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	$10.30	8.467%	$11.1721	$11.17	$11.15	$11.20
Purchase #2	$211.33	3.385%	$218.4835	$218.48	$218.50	$218.50
Purchase #3	$124.92	8.204%	$135.1684	$135.17	$135.15	$135.20
Purchase #4	$40.25	4.743%	$42.1591	$42.16	$42.15	$42.20
Purchase #5	$15.48	3.172%	$15.971	$15.97	$15.95	$16.00
Purchase #6	$20.72	3.376%	$21.4195	$21.42	$21.40	$21.40
Purchase #7	$80.34	12.390%	$90.2941	$90.29	$90.30	$90.30
7 purchase totals =	$503.34		$534.6677	$534.66	$534.60	$534.80