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	$19.56	11.586%	$21.8262	$21.83	$21.85	$21.80
Purchase #2	$130.62	6.228%	$138.755	$138.76	$138.75	$138.80
Purchase #3	$77.56	13.511%	$88.0391	$88.04	$88.05	$88.00
Purchase #4	$231.31	3.483%	$239.3665	$239.37	$239.35	$239.40
Purchase #5	$128.48	9.372%	$140.5211	$140.52	$140.50	$140.50
Purchase #6	$54.52	8.484%	$59.1455	$59.15	$59.15	$59.10
Purchase #7	$213.64	12.776%	$240.9346	$240.93	$240.95	$240.90
7 purchase totals =	$855.69		$928.5880	$928.60	$928.60	$928.50