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	$57.26	13.736%	$65.1252	$65.13	$65.15	$65.10
Purchase #2	$37.81	3.589%	$39.167	$39.17	$39.15	$39.20
Purchase #3	$203.25	8.693%	$220.9185	$220.92	$220.90	$220.90
Purchase #4	$172.61	9.700%	$189.3532	$189.35	$189.35	$189.40
Purchase #5	$177.48	10.612%	$196.3142	$196.31	$196.30	$196.30
Purchase #6	$141.83	6.212%	$150.6405	$150.64	$150.65	$150.60
Purchase #7	$128.48	6.296%	$136.5691	$136.57	$136.55	$136.60
7 purchase totals =	$918.72		$998.0877	$998.09	$998.05	$998.10