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	$42.87	4.727%	$44.8965	$44.90	$44.90	$44.90
Purchase #2	$203.53	11.837%	$227.6218	$227.62	$227.60	$227.60
Purchase #3	$89.54	7.698%	$96.4328	$96.43	$96.45	$96.40
Purchase #4	$46.45	6.426%	$49.4349	$49.43	$49.45	$49.40
Purchase #5	$35.60	12.524%	$40.0585	$40.06	$40.05	$40.10
Purchase #6	$124.77	5.265%	$131.3391	$131.34	$131.35	$131.30
Purchase #7	$78.73	4.102%	$81.9595	$81.96	$81.95	$82.00
7 purchase totals =	$621.49		$671.7431	$671.74	$671.75	$671.70