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	$226.45	5.382%	$238.6375	$238.64	$238.65	$238.60
Purchase #2	$221.68	11.204%	$246.517	$246.52	$246.50	$246.50
Purchase #3	$225.36	11.359%	$250.9586	$250.96	$250.95	$251.00
Purchase #4	$176.34	11.681%	$196.9383	$196.94	$196.95	$196.90
Purchase #5	$138.89	11.504%	$154.8679	$154.87	$154.85	$154.90
Purchase #6	$79.59	13.553%	$90.3768	$90.38	$90.40	$90.40
Purchase #7	$73.96	3.237%	$76.3541	$76.35	$76.35	$76.40
7 purchase totals =	$1,142.27		$1,254.6502	$1,254.66	$1,254.65	$1,254.70