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	$85.34	5.125%	$89.7137	$89.71	$89.70	$89.70
Purchase #2	$213.25	11.503%	$237.7801	$237.78	$237.80	$237.80
Purchase #3	$115.49	3.823%	$119.9052	$119.91	$119.90	$119.90
Purchase #4	$40.67	4.717%	$42.5884	$42.59	$42.60	$42.60
Purchase #5	$70.61	8.675%	$76.7354	$76.74	$76.75	$76.70
Purchase #6	$81.66	4.168%	$85.0636	$85.06	$85.05	$85.10
Purchase #7	$11.26	5.616%	$11.8924	$11.89	$11.90	$11.90
7 purchase totals =	$618.28		$663.6788	$663.68	$663.70	$663.70