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	$100.72	12.770%	$113.5819	$113.58	$113.60	$113.60
Purchase #2	$149.48	12.568%	$168.2666	$168.27	$168.25	$168.30
Purchase #3	$99.60	13.343%	$112.8896	$112.89	$112.90	$112.90
Purchase #4	$233.94	9.844%	$256.9691	$256.97	$256.95	$257.00
Purchase #5	$6.48	13.841%	$7.3769	$7.38	$7.40	$7.40
Purchase #6	$194.50	11.523%	$216.9122	$216.91	$216.90	$216.90
Purchase #7	$25.82	10.241%	$28.4642	$28.46	$28.45	$28.50
7 purchase totals =	$810.54		$904.4605	$904.46	$904.45	$904.60