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	$123.93	11.731%	$138.4682	$138.47	$138.45	$138.50
Purchase #2	$52.29	13.730%	$59.4694	$59.47	$59.45	$59.50
Purchase #3	$135.32	10.583%	$149.6409	$149.64	$149.65	$149.60
Purchase #4	$197.48	13.228%	$223.6027	$223.60	$223.60	$223.60
Purchase #5	$236.77	9.231%	$258.6262	$258.63	$258.65	$258.60
Purchase #6	$30.67	13.759%	$34.8899	$34.89	$34.90	$34.90
Purchase #7	$24.49	5.710%	$25.8884	$25.89	$25.90	$25.90
7 purchase totals =	$800.95		$890.5857	$890.59	$890.60	$890.60