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	$112.67	6.517%	$120.0127	$120.01	$120.00	$120.00
Purchase #2	$182.95	3.471%	$189.3002	$189.30	$189.30	$189.30
Purchase #3	$40.66	5.334%	$42.8288	$42.83	$42.85	$42.80
Purchase #4	$112.67	13.559%	$127.9469	$127.95	$127.95	$127.90
Purchase #5	$93.76	11.747%	$104.774	$104.77	$104.75	$104.80
Purchase #6	$59.45	10.448%	$65.6613	$65.66	$65.65	$65.70
Purchase #7	$198.30	13.725%	$225.5167	$225.52	$225.50	$225.50
7 purchase totals =	$800.46		$876.0406	$876.04	$876.00	$876.00