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	$128.47	7.339%	$137.8984	$137.90	$137.90	$137.90
Purchase #2	$222.74	6.833%	$237.9598	$237.96	$237.95	$238.00
Purchase #3	$58.26	9.257%	$63.6531	$63.65	$63.65	$63.70
Purchase #4	$61.90	13.620%	$70.3308	$70.33	$70.35	$70.30
Purchase #5	$59.74	9.763%	$65.5724	$65.57	$65.55	$65.60
Purchase #6	$106.88	4.103%	$111.2653	$111.27	$111.25	$111.30
Purchase #7	$141.81	11.342%	$157.8941	$157.89	$157.90	$157.90
7 purchase totals =	$779.80		$844.5739	$844.57	$844.55	$844.70