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	$122.51	7.652%	$131.8845	$131.88	$131.90	$131.90
Purchase #2	$207.76	4.240%	$216.569	$216.57	$216.55	$216.60
Purchase #3	$25.65	8.330%	$27.7866	$27.79	$27.80	$27.80
Purchase #4	$199.45	9.584%	$218.5653	$218.57	$218.55	$218.60
Purchase #5	$237.86	9.249%	$259.8597	$259.86	$259.85	$259.90
Purchase #6	$78.65	8.187%	$85.0891	$85.09	$85.10	$85.10
Purchase #7	$60.71	10.365%	$67.0026	$67.00	$67.00	$67.00
7 purchase totals =	$932.59		$1,006.7568	$1,006.76	$1,006.75	$1,006.90