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	$109.56	12.821%	$123.6067	$123.61	$123.60	$123.60
Purchase #2	$184.39	4.428%	$192.5548	$192.55	$192.55	$192.60
Purchase #3	$208.51	3.709%	$216.2436	$216.24	$216.25	$216.20
Purchase #4	$31.28	8.559%	$33.9573	$33.96	$33.95	$34.00
Purchase #5	$196.38	6.218%	$208.5909	$208.59	$208.60	$208.60
Purchase #6	$13.59	10.597%	$15.0301	$15.03	$15.05	$15.00
Purchase #7	$64.52	8.340%	$69.901	$69.90	$69.90	$69.90
7 purchase totals =	$808.23		$859.8844	$859.88	$859.90	$859.90