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	$10.72	8.777%	$11.6609	$11.66	$11.65	$11.70
Purchase #2	$175.61	7.385%	$188.5788	$188.58	$188.60	$188.60
Purchase #3	$131.42	12.228%	$147.49	$147.49	$147.50	$147.50
Purchase #4	$76.27	9.529%	$83.5378	$83.54	$83.55	$83.50
Purchase #5	$61.83	10.592%	$68.379	$68.38	$68.40	$68.40
Purchase #6	$146.46	12.329%	$164.5171	$164.52	$164.50	$164.50
Purchase #7	$123.72	12.359%	$139.0106	$139.01	$139.00	$139.00
7 purchase totals =	$726.03		$803.1742	$803.18	$803.20	$803.20