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	$82.81	10.362%	$91.3908	$91.39	$91.40	$91.40
Purchase #2	$215.59	4.117%	$224.4658	$224.47	$224.45	$224.50
Purchase #3	$94.62	7.359%	$101.5831	$101.58	$101.60	$101.60
Purchase #4	$174.65	6.700%	$186.3516	$186.35	$186.35	$186.40
Purchase #5	$165.67	5.390%	$174.5996	$174.60	$174.60	$174.60
Purchase #6	$63.96	5.645%	$67.5705	$67.57	$67.55	$67.60
Purchase #7	$102.37	3.301%	$105.7492	$105.75	$105.75	$105.70
7 purchase totals =	$899.67		$951.7106	$951.71	$951.70	$951.80