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	$63.37	7.132%	$67.8895	$67.89	$67.90	$67.90
Purchase #2	$188.90	4.173%	$196.7828	$196.78	$196.80	$196.80
Purchase #3	$201.41	5.681%	$212.8521	$212.85	$212.85	$212.90
Purchase #4	$125.99	4.749%	$131.9733	$131.97	$131.95	$132.00
Purchase #5	$224.85	3.113%	$231.8496	$231.85	$231.85	$231.80
Purchase #6	$85.34	12.414%	$95.9341	$95.93	$95.95	$95.90
Purchase #7	$210.29	3.660%	$217.9866	$217.99	$218.00	$218.00
7 purchase totals =	$1,100.15		$1,155.2680	$1,155.26	$1,155.30	$1,155.30