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	$232.29	10.333%	$256.2925	$256.29	$256.30	$256.30
Purchase #2	$191.87	13.386%	$217.5537	$217.55	$217.55	$217.60
Purchase #3	$105.38	7.726%	$113.5217	$113.52	$113.50	$113.50
Purchase #4	$168.82	7.741%	$181.8884	$181.89	$181.90	$181.90
Purchase #5	$79.90	9.404%	$87.4138	$87.41	$87.40	$87.40
Purchase #6	$200.27	13.664%	$227.6349	$227.63	$227.65	$227.60
Purchase #7	$202.43	12.143%	$227.0111	$227.01	$227.00	$227.00
7 purchase totals =	$1,180.96		$1,311.3161	$1,311.30	$1,311.30	$1,311.30