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	$132.91	10.278%	$146.5705	$146.57	$146.55	$146.60
Purchase #2	$98.39	5.589%	$103.889	$103.89	$103.90	$103.90
Purchase #3	$169.96	9.305%	$185.7748	$185.77	$185.75	$185.80
Purchase #4	$205.77	7.350%	$220.8941	$220.89	$220.90	$220.90
Purchase #5	$201.25	12.240%	$225.883	$225.88	$225.90	$225.90
Purchase #6	$212.48	8.209%	$229.9225	$229.92	$229.90	$229.90
Purchase #7	$156.85	12.636%	$176.6696	$176.67	$176.65	$176.70
7 purchase totals =	$1,177.61		$1,289.6035	$1,289.59	$1,289.55	$1,289.70