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	$143.88	9.600%	$157.6925	$157.69	$157.70	$157.70
Purchase #2	$110.88	11.739%	$123.8962	$123.90	$123.90	$123.90
Purchase #3	$99.89	10.696%	$110.5742	$110.57	$110.55	$110.60
Purchase #4	$123.95	6.123%	$131.5395	$131.54	$131.55	$131.50
Purchase #5	$40.55	5.770%	$42.8897	$42.89	$42.90	$42.90
Purchase #6	$242.94	12.272%	$272.7536	$272.75	$272.75	$272.80
Purchase #7	$138.29	3.361%	$142.9379	$142.94	$142.95	$142.90
7 purchase totals =	$900.38		$982.2836	$982.28	$982.30	$982.30