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	$82.29	10.366%	$90.8202	$90.82	$90.80	$90.80
Purchase #2	$20.66	10.593%	$22.8485	$22.85	$22.85	$22.80
Purchase #3	$119.85	9.290%	$130.9841	$130.98	$131.00	$131.00
Purchase #4	$10.66	5.856%	$11.2842	$11.28	$11.30	$11.30
Purchase #5	$176.72	10.583%	$195.4223	$195.42	$195.40	$195.40
Purchase #6	$88.54	6.157%	$93.9914	$93.99	$94.00	$94.00
Purchase #7	$88.42	13.788%	$100.6113	$100.61	$100.60	$100.60
7 purchase totals =	$587.14		$645.9620	$645.95	$645.95	$645.90