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	$127.87	5.510%	$134.9156	$134.92	$134.90	$134.90
Purchase #2	$139.91	13.868%	$159.3127	$159.31	$159.30	$159.30
Purchase #3	$243.27	11.497%	$271.2388	$271.24	$271.25	$271.20
Purchase #4	$117.47	8.174%	$127.072	$127.07	$127.05	$127.10
Purchase #5	$123.42	10.212%	$136.0237	$136.02	$136.00	$136.00
Purchase #6	$208.27	8.287%	$225.5293	$225.53	$225.55	$225.50
Purchase #7	$133.65	12.448%	$150.2868	$150.29	$150.30	$150.30
7 purchase totals =	$1,093.86		$1,204.3789	$1,204.38	$1,204.35	$1,204.30