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	$77.65	13.227%	$87.9208	$87.92	$87.90	$87.90
Purchase #2	$21.39	3.193%	$22.073	$22.07	$22.05	$22.10
Purchase #3	$38.45	4.146%	$40.0441	$40.04	$40.05	$40.00
Purchase #4	$139.86	3.117%	$144.2194	$144.22	$144.20	$144.20
Purchase #5	$200.79	10.282%	$221.4352	$221.44	$221.45	$221.40
Purchase #6	$196.30	6.736%	$209.5228	$209.52	$209.50	$209.50
Purchase #7	$71.45	6.852%	$76.3458	$76.35	$76.35	$76.30
7 purchase totals =	$745.89		$801.5611	$801.56	$801.50	$801.40