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	$229.29	11.415%	$255.4635	$255.46	$255.45	$255.50
Purchase #2	$42.57	7.155%	$45.6159	$45.62	$45.60	$45.60
Purchase #3	$44.80	12.108%	$50.2244	$50.22	$50.20	$50.20
Purchase #4	$98.32	4.351%	$102.5979	$102.60	$102.60	$102.60
Purchase #5	$204.37	4.195%	$212.9433	$212.94	$212.95	$212.90
Purchase #6	$75.66	3.849%	$78.5722	$78.57	$78.55	$78.60
Purchase #7	$140.75	4.377%	$146.9106	$146.91	$146.90	$146.90
7 purchase totals =	$835.76		$892.3278	$892.32	$892.25	$892.30