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	$130.25	6.171%	$138.2877	$138.29	$138.30	$138.30
Purchase #2	$227.31	6.861%	$242.9057	$242.91	$242.90	$242.90
Purchase #3	$40.46	13.422%	$45.8905	$45.89	$45.90	$45.90
Purchase #4	$214.74	4.798%	$225.0432	$225.04	$225.05	$225.00
Purchase #5	$221.61	13.689%	$251.9462	$251.95	$251.95	$251.90
Purchase #6	$5.45	10.196%	$6.0057	$6.01	$6.00	$6.00
Purchase #7	$83.37	6.770%	$89.0141	$89.01	$89.00	$89.00
7 purchase totals =	$923.19		$999.0931	$999.10	$999.10	$999.00