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	$144.82	13.274%	$164.0434	$164.04	$164.05	$164.00
Purchase #2	$64.38	5.509%	$67.9267	$67.93	$67.95	$67.90
Purchase #3	$183.58	3.773%	$190.5065	$190.51	$190.50	$190.50
Purchase #4	$135.89	4.709%	$142.2891	$142.29	$142.30	$142.30
Purchase #5	$164.93	13.270%	$186.8162	$186.82	$186.80	$186.80
Purchase #6	$57.72	10.629%	$63.8551	$63.86	$63.85	$63.90
Purchase #7	$172.98	7.400%	$185.7805	$185.78	$185.80	$185.80
7 purchase totals =	$924.30		$1,001.2175	$1,001.23	$1,001.25	$1,001.20