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	$39.79	7.723%	$42.863	$42.86	$42.85	$42.90
Purchase #2	$20.34	6.848%	$21.7329	$21.73	$21.75	$21.70
Purchase #3	$139.52	12.526%	$156.9963	$157.00	$157.00	$157.00
Purchase #4	$241.32	13.254%	$273.3046	$273.30	$273.30	$273.30
Purchase #5	$30.96	7.658%	$33.3309	$33.33	$33.35	$33.30
Purchase #6	$18.33	13.204%	$20.7503	$20.75	$20.75	$20.80
Purchase #7	$171.26	11.624%	$191.1673	$191.17	$191.15	$191.20
7 purchase totals =	$661.52		$740.1453	$740.14	$740.15	$740.20