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	12.488%	$123.0056	$123.01	$123.00	$123.00
Purchase #2	$92.96	13.864%	$105.848	$105.85	$105.85	$105.80
Purchase #3	$185.49	7.530%	$199.4574	$199.46	$199.45	$199.50
Purchase #4	$100.32	5.564%	$105.9018	$105.90	$105.90	$105.90
Purchase #5	$239.29	11.619%	$267.0931	$267.09	$267.10	$267.10
Purchase #6	$15.56	12.463%	$17.4992	$17.50	$17.50	$17.50
Purchase #7	$189.54	12.348%	$212.9444	$212.94	$212.95	$212.90
7 purchase totals =	$932.51		$1,031.7495	$1,031.75	$1,031.75	$1,031.70