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	$24.31	12.681%	$27.3928	$27.39	$27.40	$27.40
Purchase #2	$147.90	11.683%	$165.1792	$165.18	$165.20	$165.20
Purchase #3	$111.90	7.168%	$119.921	$119.92	$119.90	$119.90
Purchase #4	$121.95	3.763%	$126.539	$126.54	$126.55	$126.50
Purchase #5	$37.43	10.484%	$41.3542	$41.35	$41.35	$41.40
Purchase #6	$84.48	3.385%	$87.3396	$87.34	$87.35	$87.30
Purchase #7	$81.74	4.538%	$85.4494	$85.45	$85.45	$85.40
7 purchase totals =	$609.71		$653.1752	$653.17	$653.20	$653.10