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	$150.52	13.168%	$170.3405	$170.34	$170.35	$170.30
Purchase #2	$68.46	5.808%	$72.4362	$72.44	$72.45	$72.40
Purchase #3	$14.37	5.248%	$15.1241	$15.12	$15.10	$15.10
Purchase #4	$194.67	3.222%	$200.9423	$200.94	$200.95	$200.90
Purchase #5	$62.45	7.332%	$67.0288	$67.03	$67.05	$67.00
Purchase #6	$87.57	3.167%	$90.3433	$90.34	$90.35	$90.30
Purchase #7	$40.52	8.456%	$43.9464	$43.95	$43.95	$43.90
7 purchase totals =	$618.56		$660.1616	$660.16	$660.20	$659.90