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	$122.95	13.762%	$139.8704	$139.87	$139.85	$139.90
Purchase #2	$154.30	7.483%	$165.8463	$165.85	$165.85	$165.80
Purchase #3	$79.56	9.437%	$87.0681	$87.07	$87.05	$87.10
Purchase #4	$11.64	6.131%	$12.3536	$12.35	$12.35	$12.40
Purchase #5	$67.70	4.756%	$70.9198	$70.92	$70.90	$70.90
Purchase #6	$141.44	6.689%	$150.9009	$150.90	$150.90	$150.90
Purchase #7	$28.31	10.874%	$31.3884	$31.39	$31.40	$31.40
7 purchase totals =	$605.90		$658.3475	$658.35	$658.30	$658.40