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	$135.89	10.387%	$150.0049	$150.00	$150.00	$150.00
Purchase #2	$37.89	10.492%	$41.8654	$41.87	$41.85	$41.90
Purchase #3	$106.35	11.831%	$118.9323	$118.93	$118.95	$118.90
Purchase #4	$123.54	11.441%	$137.6742	$137.67	$137.65	$137.70
Purchase #5	$131.82	6.154%	$139.9322	$139.93	$139.95	$139.90
Purchase #6	$173.72	9.866%	$190.8592	$190.86	$190.85	$190.90
Purchase #7	$59.56	13.633%	$67.6798	$67.68	$67.70	$67.70
7 purchase totals =	$768.77		$846.9480	$846.94	$846.95	$847.00