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	$27.48	7.719%	$29.6012	$29.60	$29.60	$29.60
Purchase #2	$119.37	7.541%	$128.3717	$128.37	$128.35	$128.40
Purchase #3	$42.57	3.265%	$43.9599	$43.96	$43.95	$44.00
Purchase #4	$64.76	4.375%	$67.5933	$67.59	$67.60	$67.60
Purchase #5	$230.33	3.119%	$237.514	$237.51	$237.50	$237.50
Purchase #6	$144.33	4.533%	$150.8725	$150.87	$150.85	$150.90
Purchase #7	$216.92	11.525%	$241.92	$241.92	$241.90	$241.90
7 purchase totals =	$845.76		$899.8326	$899.82	$899.75	$899.90