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	$52.85	13.150%	$59.7998	$59.80	$59.80	$59.80
Purchase #2	$43.54	3.555%	$45.0878	$45.09	$45.10	$45.10
Purchase #3	$92.39	11.200%	$102.7377	$102.74	$102.75	$102.70
Purchase #4	$17.42	7.544%	$18.7342	$18.73	$18.75	$18.70
Purchase #5	$67.42	8.457%	$73.1217	$73.12	$73.10	$73.10
Purchase #6	$102.81	10.761%	$113.8734	$113.87	$113.85	$113.90
Purchase #7	$246.32	9.853%	$270.5899	$270.59	$270.60	$270.60
7 purchase totals =	$622.75		$683.9445	$683.94	$683.95	$683.90