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	$143.63	12.423%	$161.4732	$161.47	$161.45	$161.50
Purchase #2	$75.91	3.626%	$78.6625	$78.66	$78.65	$78.70
Purchase #3	$104.67	11.366%	$116.5668	$116.57	$116.55	$116.60
Purchase #4	$186.96	6.201%	$198.5534	$198.55	$198.55	$198.60
Purchase #5	$55.34	4.378%	$57.7628	$57.76	$57.75	$57.80
Purchase #6	$78.40	6.856%	$83.7751	$83.78	$83.80	$83.80
Purchase #7	$48.32	9.309%	$52.8181	$52.82	$52.80	$52.80
7 purchase totals =	$693.23		$749.6119	$749.61	$749.55	$749.80