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	$30.36	3.110%	$31.3042	$31.30	$31.30	$31.30
Purchase #2	$219.87	11.375%	$244.8802	$244.88	$244.90	$244.90
Purchase #3	$37.38	8.728%	$40.6425	$40.64	$40.65	$40.60
Purchase #4	$231.29	10.654%	$255.9316	$255.93	$255.95	$255.90
Purchase #5	$208.77	8.874%	$227.2962	$227.30	$227.30	$227.30
Purchase #6	$90.93	4.448%	$94.9746	$94.97	$94.95	$95.00
Purchase #7	$38.75	5.177%	$40.7561	$40.76	$40.75	$40.80
7 purchase totals =	$857.35		$935.7854	$935.78	$935.80	$935.80