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	$180.43	3.129%	$186.0757	$186.08	$186.10	$186.10
Purchase #2	$56.83	8.175%	$61.4759	$61.48	$61.50	$61.50
Purchase #3	$165.30	13.694%	$187.9362	$187.94	$187.95	$187.90
Purchase #4	$169.85	3.395%	$175.6164	$175.62	$175.60	$175.60
Purchase #5	$36.80	3.140%	$37.9555	$37.96	$37.95	$38.00
Purchase #6	$10.89	5.761%	$11.5174	$11.52	$11.50	$11.50
Purchase #7	$186.27	12.698%	$209.9226	$209.92	$209.90	$209.90
7 purchase totals =	$806.37		$870.4997	$870.52	$870.50	$870.50