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	$161.74	3.808%	$167.8991	$167.90	$167.90	$167.90
Purchase #2	$104.59	5.816%	$110.673	$110.67	$110.65	$110.70
Purchase #3	$154.46	6.144%	$163.95	$163.95	$163.95	$164.00
Purchase #4	$78.57	8.801%	$85.4849	$85.48	$85.50	$85.50
Purchase #5	$10.55	3.189%	$10.8864	$10.89	$10.90	$10.90
Purchase #6	$208.58	6.833%	$222.8323	$222.83	$222.85	$222.80
Purchase #7	$72.33	12.670%	$81.4942	$81.49	$81.50	$81.50
7 purchase totals =	$790.82		$843.2199	$843.21	$843.25	$843.30