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	$59.96	13.305%	$67.9377	$67.94	$67.95	$67.90
Purchase #2	$35.50	11.217%	$39.482	$39.48	$39.50	$39.50
Purchase #3	$228.95	9.854%	$251.5107	$251.51	$251.50	$251.50
Purchase #4	$11.94	6.293%	$12.6914	$12.69	$12.70	$12.70
Purchase #5	$65.25	12.450%	$73.3736	$73.37	$73.35	$73.40
Purchase #6	$6.77	9.721%	$7.4281	$7.43	$7.45	$7.40
Purchase #7	$176.86	6.304%	$188.0093	$188.01	$188.00	$188.00
7 purchase totals =	$585.23		$640.4328	$640.43	$640.45	$640.40