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	$239.42	4.519%	$250.2394	$250.24	$250.25	$250.20
Purchase #2	$63.45	4.781%	$66.4835	$66.48	$66.50	$66.50
Purchase #3	$211.77	7.406%	$227.4537	$227.45	$227.45	$227.50
Purchase #4	$94.71	11.691%	$105.7825	$105.78	$105.80	$105.80
Purchase #5	$39.87	11.312%	$44.3801	$44.38	$44.40	$44.40
Purchase #6	$207.31	5.453%	$218.6146	$218.61	$218.60	$218.60
Purchase #7	$73.69	6.713%	$78.6368	$78.64	$78.65	$78.60
7 purchase totals =	$930.22		$991.5906	$991.58	$991.65	$991.60