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	$12.79	3.220%	$13.2018	$13.20	$13.20	$13.20
Purchase #2	$165.76	4.733%	$173.6054	$173.61	$173.60	$173.60
Purchase #3	$139.73	10.267%	$154.0761	$154.08	$154.10	$154.10
Purchase #4	$145.38	13.397%	$164.8566	$164.86	$164.85	$164.90
Purchase #5	$249.46	9.859%	$274.0543	$274.05	$274.05	$274.10
Purchase #6	$133.89	13.542%	$152.0214	$152.02	$152.00	$152.00
Purchase #7	$169.34	9.638%	$185.661	$185.66	$185.65	$185.70
7 purchase totals =	$1,016.35		$1,117.4766	$1,117.48	$1,117.45	$1,117.60