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	$30.46	10.359%	$33.6154	$33.62	$33.60	$33.60
Purchase #2	$38.36	9.389%	$41.9616	$41.96	$41.95	$42.00
Purchase #3	$200.68	12.503%	$225.771	$225.77	$225.75	$225.80
Purchase #4	$59.94	10.417%	$66.1839	$66.18	$66.20	$66.20
Purchase #5	$164.50	10.326%	$181.4863	$181.49	$181.50	$181.50
Purchase #6	$180.60	10.503%	$199.5684	$199.57	$199.55	$199.60
Purchase #7	$75.86	12.669%	$85.4707	$85.47	$85.45	$85.50
7 purchase totals =	$750.40		$834.0573	$834.06	$834.00	$834.20