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	$219.45	12.825%	$247.5945	$247.59	$247.60	$247.60
Purchase #2	$43.85	4.409%	$45.7833	$45.78	$45.80	$45.80
Purchase #3	$116.88	13.392%	$132.5326	$132.53	$132.55	$132.50
Purchase #4	$183.56	5.467%	$193.5952	$193.60	$193.60	$193.60
Purchase #5	$65.83	9.650%	$72.1826	$72.18	$72.20	$72.20
Purchase #6	$149.36	6.103%	$158.4754	$158.48	$158.50	$158.50
Purchase #7	$50.39	4.449%	$52.6319	$52.63	$52.65	$52.60
7 purchase totals =	$829.32		$902.7955	$902.79	$902.90	$902.80