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	$240.75	12.514%	$270.8775	$270.88	$270.90	$270.90
Purchase #2	$213.56	11.196%	$237.4702	$237.47	$237.45	$237.50
Purchase #3	$25.87	7.390%	$27.7818	$27.78	$27.80	$27.80
Purchase #4	$80.38	11.784%	$89.852	$89.85	$89.85	$89.90
Purchase #5	$221.71	13.450%	$251.53	$251.53	$251.55	$251.50
Purchase #6	$25.35	11.118%	$28.1684	$28.17	$28.15	$28.20
Purchase #7	$43.55	6.196%	$46.2484	$46.25	$46.25	$46.20
7 purchase totals =	$851.17		$951.9283	$951.93	$951.95	$952.00