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	$102.97	3.308%	$106.3762	$106.38	$106.40	$106.40
Purchase #2	$199.31	10.672%	$220.5804	$220.58	$220.60	$220.60
Purchase #3	$90.33	3.531%	$93.5196	$93.52	$93.50	$93.50
Purchase #4	$10.61	3.182%	$10.9476	$10.95	$10.95	$10.90
Purchase #5	$87.72	3.633%	$90.9069	$90.91	$90.90	$90.90
Purchase #6	$170.75	5.115%	$179.4839	$179.48	$179.50	$179.50
Purchase #7	$98.60	13.441%	$111.8528	$111.85	$111.85	$111.90
7 purchase totals =	$760.29		$813.6674	$813.67	$813.70	$813.70