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	$87.58	3.414%	$90.57	$90.57	$90.55	$90.60
Purchase #2	$82.59	11.838%	$92.367	$92.37	$92.35	$92.40
Purchase #3	$236.63	5.694%	$250.1037	$250.10	$250.10	$250.10
Purchase #4	$34.69	9.207%	$37.8839	$37.88	$37.90	$37.90
Purchase #5	$228.37	9.843%	$250.8485	$250.85	$250.85	$250.80
Purchase #6	$209.43	3.830%	$217.4512	$217.45	$217.45	$217.50
Purchase #7	$36.78	6.525%	$39.1799	$39.18	$39.20	$39.20
7 purchase totals =	$916.07		$978.4042	$978.40	$978.40	$978.50