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	$106.93	5.702%	$113.0271	$113.03	$113.05	$113.00
Purchase #2	$242.60	3.303%	$250.6131	$250.61	$250.60	$250.60
Purchase #3	$62.31	10.457%	$68.8258	$68.83	$68.85	$68.80
Purchase #4	$155.43	3.291%	$160.5452	$160.55	$160.55	$160.50
Purchase #5	$38.40	7.421%	$41.2497	$41.25	$41.25	$41.20
Purchase #6	$166.29	3.807%	$172.6207	$172.62	$172.60	$172.60
Purchase #7	$84.42	13.194%	$95.5584	$95.56	$95.55	$95.60
7 purchase totals =	$856.38		$902.4400	$902.45	$902.45	$902.30