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	$6.60	10.606%	$7.3	$7.30	$7.30	$7.30
Purchase #2	$67.70	9.136%	$73.8851	$73.89	$73.90	$73.90
Purchase #3	$131.58	5.853%	$139.2814	$139.28	$139.30	$139.30
Purchase #4	$132.75	10.841%	$147.1414	$147.14	$147.15	$147.10
Purchase #5	$50.79	11.559%	$56.6608	$56.66	$56.65	$56.70
Purchase #6	$168.48	10.164%	$185.6043	$185.60	$185.60	$185.60
Purchase #7	$52.61	12.632%	$59.2557	$59.26	$59.25	$59.30
7 purchase totals =	$610.51		$669.1287	$669.13	$669.15	$669.20