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	$39.96	3.599%	$41.3982	$41.40	$41.40	$41.40
Purchase #2	$36.31	10.423%	$40.0946	$40.09	$40.10	$40.10
Purchase #3	$190.63	12.700%	$214.84	$214.84	$214.85	$214.80
Purchase #4	$70.54	3.374%	$72.92	$72.92	$72.90	$72.90
Purchase #5	$183.54	11.237%	$204.1644	$204.16	$204.15	$204.20
Purchase #6	$63.68	6.482%	$67.8077	$67.81	$67.80	$67.80
Purchase #7	$31.37	6.150%	$33.2993	$33.30	$33.30	$33.30
7 purchase totals =	$616.03		$674.5242	$674.52	$674.50	$674.50