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	$42.93	6.232%	$45.6054	$45.61	$45.60	$45.60
Purchase #2	$128.93	6.560%	$137.3878	$137.39	$137.40	$137.40
Purchase #3	$112.85	5.484%	$119.0387	$119.04	$119.05	$119.00
Purchase #4	$30.83	8.570%	$33.4721	$33.47	$33.45	$33.50
Purchase #5	$219.28	13.344%	$248.5407	$248.54	$248.55	$248.50
Purchase #6	$174.25	6.862%	$186.207	$186.21	$186.20	$186.20
Purchase #7	$78.88	4.674%	$82.5669	$82.57	$82.55	$82.60
7 purchase totals =	$787.95		$852.8186	$852.83	$852.80	$852.80