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	$29.62	13.151%	$33.5153	$33.52	$33.50	$33.50
Purchase #2	$85.72	5.290%	$90.2546	$90.25	$90.25	$90.30
Purchase #3	$47.63	6.775%	$50.8569	$50.86	$50.85	$50.90
Purchase #4	$201.65	13.478%	$228.8284	$228.83	$228.85	$228.80
Purchase #5	$176.97	9.519%	$193.8158	$193.82	$193.80	$193.80
Purchase #6	$91.37	8.390%	$99.0359	$99.04	$99.05	$99.00
Purchase #7	$183.42	3.811%	$190.4101	$190.41	$190.40	$190.40
7 purchase totals =	$816.38		$886.7170	$886.73	$886.70	$886.70