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	$120.98	8.628%	$131.4182	$131.42	$131.40	$131.40
Purchase #2	$154.57	6.338%	$164.3666	$164.37	$164.35	$164.40
Purchase #3	$116.34	12.646%	$131.0524	$131.05	$131.05	$131.10
Purchase #4	$74.87	13.698%	$85.1257	$85.13	$85.15	$85.10
Purchase #5	$169.82	11.438%	$189.244	$189.24	$189.25	$189.20
Purchase #6	$139.60	6.528%	$148.7131	$148.71	$148.70	$148.70
Purchase #7	$199.29	13.792%	$226.7761	$226.78	$226.80	$226.80
7 purchase totals =	$975.47		$1,076.6961	$1,076.70	$1,076.70	$1,076.70