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	$204.66	6.660%	$218.2904	$218.29	$218.30	$218.30
Purchase #2	$81.93	12.104%	$91.8468	$91.85	$91.85	$91.80
Purchase #3	$169.29	9.838%	$185.9448	$185.94	$185.95	$185.90
Purchase #4	$170.92	3.278%	$176.5228	$176.52	$176.50	$176.50
Purchase #5	$66.83	3.587%	$69.2272	$69.23	$69.25	$69.20
Purchase #6	$32.43	13.684%	$36.8677	$36.87	$36.85	$36.90
Purchase #7	$134.43	8.525%	$145.8902	$145.89	$145.90	$145.90
7 purchase totals =	$860.49		$924.5899	$924.59	$924.60	$924.50