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	$103.94	13.200%	$117.6601	$117.66	$117.65	$117.70
Purchase #2	$50.81	3.595%	$52.6366	$52.64	$52.65	$52.60
Purchase #3	$130.44	10.861%	$144.6071	$144.61	$144.60	$144.60
Purchase #4	$28.33	12.344%	$31.8271	$31.83	$31.85	$31.80
Purchase #5	$248.57	9.278%	$271.6323	$271.63	$271.65	$271.60
Purchase #6	$55.61	10.701%	$61.5608	$61.56	$61.55	$61.60
Purchase #7	$28.30	12.716%	$31.8986	$31.90	$31.90	$31.90
7 purchase totals =	$646.00		$711.8226	$711.83	$711.85	$711.80