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	$195.89	13.525%	$222.3841	$222.38	$222.40	$222.40
Purchase #2	$212.66	13.299%	$240.9417	$240.94	$240.95	$240.90
Purchase #3	$116.86	10.276%	$128.8685	$128.87	$128.85	$128.90
Purchase #4	$225.86	13.151%	$255.5628	$255.56	$255.55	$255.60
Purchase #5	$107.83	13.652%	$122.551	$122.55	$122.55	$122.60
Purchase #6	$68.56	12.570%	$77.178	$77.18	$77.20	$77.20
Purchase #7	$229.93	8.286%	$248.982	$248.98	$249.00	$249.00
7 purchase totals =	$1,157.59		$1,296.4681	$1,296.46	$1,296.50	$1,296.60