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	$123.31	12.513%	$138.7398	$138.74	$138.75	$138.70
Purchase #2	$244.39	6.753%	$260.8937	$260.89	$260.90	$260.90
Purchase #3	$112.46	3.415%	$116.3005	$116.30	$116.30	$116.30
Purchase #4	$111.29	7.865%	$120.043	$120.04	$120.05	$120.00
Purchase #5	$156.53	12.730%	$176.4563	$176.46	$176.45	$176.50
Purchase #6	$160.46	7.568%	$172.6036	$172.60	$172.60	$172.60
Purchase #7	$215.25	12.691%	$242.5674	$242.57	$242.55	$242.60
7 purchase totals =	$1,123.69		$1,227.6043	$1,227.60	$1,227.60	$1,227.60