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	$129.66	11.624%	$144.7317	$144.73	$144.75	$144.70
Purchase #2	$100.84	10.385%	$111.3122	$111.31	$111.30	$111.30
Purchase #3	$44.87	4.811%	$47.0287	$47.03	$47.05	$47.00
Purchase #4	$62.30	5.104%	$65.4798	$65.48	$65.50	$65.50
Purchase #5	$135.39	3.696%	$140.394	$140.39	$140.40	$140.40
Purchase #6	$208.83	7.118%	$223.6945	$223.69	$223.70	$223.70
Purchase #7	$62.93	5.739%	$66.5416	$66.54	$66.55	$66.50
7 purchase totals =	$744.82		$799.1825	$799.17	$799.25	$799.10