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	$112.61	10.515%	$124.4509	$124.45	$124.45	$124.50
Purchase #2	$65.49	5.644%	$69.1863	$69.19	$69.20	$69.20
Purchase #3	$134.53	4.518%	$140.6081	$140.61	$140.60	$140.60
Purchase #4	$233.59	13.812%	$265.8535	$265.85	$265.85	$265.90
Purchase #5	$80.33	10.179%	$88.5068	$88.51	$88.50	$88.50
Purchase #6	$60.36	3.552%	$62.504	$62.50	$62.50	$62.50
Purchase #7	$153.48	5.767%	$162.3312	$162.33	$162.35	$162.30
7 purchase totals =	$840.39		$913.4408	$913.44	$913.45	$913.50