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	$177.58	11.715%	$198.3835	$198.38	$198.40	$198.40
Purchase #2	$123.83	5.414%	$130.5342	$130.53	$130.55	$130.50
Purchase #3	$248.33	9.561%	$272.0728	$272.07	$272.05	$272.10
Purchase #4	$109.50	12.337%	$123.009	$123.01	$123.00	$123.00
Purchase #5	$131.92	9.122%	$143.9537	$143.95	$143.95	$144.00
Purchase #6	$48.30	7.496%	$51.9206	$51.92	$51.90	$51.90
Purchase #7	$48.27	4.352%	$50.3707	$50.37	$50.35	$50.40
7 purchase totals =	$887.73		$970.2445	$970.23	$970.20	$970.30