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	$233.38	7.272%	$250.3514	$250.35	$250.35	$250.40
Purchase #2	$40.99	4.437%	$42.8087	$42.81	$42.80	$42.80
Purchase #3	$113.58	5.137%	$119.4146	$119.41	$119.40	$119.40
Purchase #4	$174.29	6.600%	$185.7931	$185.79	$185.80	$185.80
Purchase #5	$42.83	5.166%	$45.0426	$45.04	$45.05	$45.00
Purchase #6	$102.32	3.249%	$105.6444	$105.64	$105.65	$105.60
Purchase #7	$57.84	4.714%	$60.5666	$60.57	$60.55	$60.60
7 purchase totals =	$765.23		$809.6214	$809.61	$809.60	$809.60