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	$143.29	13.474%	$162.5969	$162.60	$162.60	$162.60
Purchase #2	$176.45	11.472%	$196.6923	$196.69	$196.70	$196.70
Purchase #3	$87.93	3.333%	$90.8607	$90.86	$90.85	$90.90
Purchase #4	$236.78	4.725%	$247.9679	$247.97	$247.95	$248.00
Purchase #5	$87.54	9.556%	$95.9053	$95.91	$95.90	$95.90
Purchase #6	$50.98	12.400%	$57.3015	$57.30	$57.30	$57.30
Purchase #7	$74.46	12.230%	$83.5665	$83.57	$83.55	$83.60
7 purchase totals =	$857.43		$934.8911	$934.90	$934.85	$935.00