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	$125.89	8.674%	$136.8097	$136.81	$136.80	$136.80
Purchase #2	$135.83	7.148%	$145.5391	$145.54	$145.55	$145.50
Purchase #3	$132.69	13.567%	$150.6921	$150.69	$150.70	$150.70
Purchase #4	$18.47	6.466%	$19.6643	$19.66	$19.65	$19.70
Purchase #5	$117.70	11.284%	$130.9813	$130.98	$131.00	$131.00
Purchase #6	$173.78	8.645%	$188.8033	$188.80	$188.80	$188.80
Purchase #7	$57.49	4.140%	$59.8701	$59.87	$59.85	$59.90
7 purchase totals =	$761.85		$832.3599	$832.35	$832.35	$832.40