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	$109.35	9.361%	$119.5863	$119.59	$119.60	$119.60
Purchase #2	$55.90	9.707%	$61.3262	$61.33	$61.35	$61.30
Purchase #3	$58.73	12.135%	$65.8569	$65.86	$65.85	$65.90
Purchase #4	$209.45	8.692%	$227.6554	$227.66	$227.65	$227.70
Purchase #5	$148.60	7.622%	$159.9263	$159.93	$159.95	$159.90
Purchase #6	$213.48	4.225%	$222.4995	$222.50	$222.50	$222.50
Purchase #7	$39.70	8.326%	$43.0054	$43.01	$43.00	$43.00
7 purchase totals =	$835.21		$899.8560	$899.88	$899.90	$899.90