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	$30.28	10.777%	$33.5433	$33.54	$33.55	$33.50
Purchase #2	$82.48	10.298%	$90.9738	$90.97	$90.95	$91.00
Purchase #3	$41.93	10.857%	$46.4823	$46.48	$46.50	$46.50
Purchase #4	$136.50	6.325%	$145.1336	$145.13	$145.15	$145.10
Purchase #5	$124.79	6.359%	$132.7254	$132.73	$132.75	$132.70
Purchase #6	$30.92	4.105%	$32.1893	$32.19	$32.20	$32.20
Purchase #7	$6.45	12.324%	$7.2449	$7.24	$7.25	$7.20
7 purchase totals =	$453.35		$488.2926	$488.28	$488.35	$488.20