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	$225.99	13.855%	$257.3009	$257.30	$257.30	$257.30
Purchase #2	$212.50	11.123%	$236.1364	$236.14	$236.15	$236.10
Purchase #3	$149.72	4.610%	$156.6221	$156.62	$156.60	$156.60
Purchase #4	$143.86	13.199%	$162.8481	$162.85	$162.85	$162.80
Purchase #5	$236.94	8.419%	$256.888	$256.89	$256.90	$256.90
Purchase #6	$121.94	11.853%	$136.3935	$136.39	$136.40	$136.40
Purchase #7	$37.78	13.674%	$42.946	$42.95	$42.95	$42.90
7 purchase totals =	$1,128.73		$1,249.1350	$1,249.14	$1,249.15	$1,249.00