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	$119.57	9.202%	$130.5728	$130.57	$130.55	$130.60
Purchase #2	$176.49	11.446%	$196.691	$196.69	$196.70	$196.70
Purchase #3	$13.90	9.555%	$15.2281	$15.23	$15.25	$15.20
Purchase #4	$100.46	6.746%	$107.237	$107.24	$107.25	$107.20
Purchase #5	$65.61	12.132%	$73.5698	$73.57	$73.55	$73.60
Purchase #6	$18.89	6.841%	$20.1823	$20.18	$20.20	$20.20
Purchase #7	$88.31	12.529%	$99.3744	$99.37	$99.35	$99.40
7 purchase totals =	$583.23		$642.8554	$642.85	$642.85	$642.90