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	$6.37	5.756%	$6.7367	$6.74	$6.75	$6.70
Purchase #2	$144.35	8.198%	$156.1838	$156.18	$156.20	$156.20
Purchase #3	$61.72	12.335%	$69.3332	$69.33	$69.35	$69.30
Purchase #4	$168.64	13.652%	$191.6627	$191.66	$191.65	$191.70
Purchase #5	$102.96	8.391%	$111.5994	$111.60	$111.60	$111.60
Purchase #6	$114.79	8.243%	$124.2521	$124.25	$124.25	$124.30
Purchase #7	$72.64	8.497%	$78.8122	$78.81	$78.80	$78.80
7 purchase totals =	$671.47		$738.5801	$738.57	$738.60	$738.60