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	$172.29	6.721%	$183.8696	$183.87	$183.85	$183.90
Purchase #2	$208.53	6.421%	$221.9197	$221.92	$221.90	$221.90
Purchase #3	$10.54	13.243%	$11.9358	$11.94	$11.95	$11.90
Purchase #4	$178.36	8.683%	$193.847	$193.85	$193.85	$193.80
Purchase #5	$99.46	6.175%	$105.6017	$105.60	$105.60	$105.60
Purchase #6	$84.81	7.195%	$90.9121	$90.91	$90.90	$90.90
Purchase #7	$134.57	11.531%	$150.0873	$150.09	$150.10	$150.10
7 purchase totals =	$888.56		$958.1732	$958.18	$958.15	$958.10