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	$236.53	10.319%	$260.9375	$260.94	$260.95	$260.90
Purchase #2	$40.49	4.808%	$42.4368	$42.44	$42.45	$42.40
Purchase #3	$14.32	6.246%	$15.2144	$15.21	$15.20	$15.20
Purchase #4	$86.52	10.456%	$95.5665	$95.57	$95.55	$95.60
Purchase #5	$13.71	10.569%	$15.159	$15.16	$15.15	$15.20
Purchase #6	$90.38	11.620%	$100.8822	$100.88	$100.90	$100.90
Purchase #7	$98.53	4.275%	$102.7422	$102.74	$102.75	$102.70
7 purchase totals =	$580.48		$632.9386	$632.94	$632.95	$632.90