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	$208.69	10.832%	$231.2953	$231.30	$231.30	$231.30
Purchase #2	$121.56	12.728%	$137.0322	$137.03	$137.05	$137.00
Purchase #3	$58.34	9.526%	$63.8975	$63.90	$63.90	$63.90
Purchase #4	$39.39	11.189%	$43.7973	$43.80	$43.80	$43.80
Purchase #5	$31.93	6.302%	$33.9422	$33.94	$33.95	$33.90
Purchase #6	$45.89	9.147%	$50.0876	$50.09	$50.10	$50.10
Purchase #7	$139.71	3.299%	$144.319	$144.32	$144.30	$144.30
7 purchase totals =	$645.51		$704.3711	$704.38	$704.40	$704.30