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	$82.98	9.196%	$90.6108	$90.61	$90.60	$90.60
Purchase #2	$69.53	8.526%	$75.4581	$75.46	$75.45	$75.50
Purchase #3	$80.37	11.723%	$89.7918	$89.79	$89.80	$89.80
Purchase #4	$37.84	6.166%	$40.1732	$40.17	$40.15	$40.20
Purchase #5	$184.94	9.234%	$202.0174	$202.02	$202.00	$202.00
Purchase #6	$62.34	6.321%	$66.2805	$66.28	$66.30	$66.30
Purchase #7	$192.96	3.198%	$199.1309	$199.13	$199.15	$199.10
7 purchase totals =	$710.96		$763.4627	$763.46	$763.45	$763.50