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	$14.27	11.297%	$15.8821	$15.88	$15.90	$15.90
Purchase #2	$41.30	9.406%	$45.1847	$45.18	$45.20	$45.20
Purchase #3	$242.34	13.437%	$274.9032	$274.90	$274.90	$274.90
Purchase #4	$97.30	11.326%	$108.3202	$108.32	$108.30	$108.30
Purchase #5	$180.50	3.169%	$186.22	$186.22	$186.20	$186.20
Purchase #6	$139.72	7.433%	$150.1054	$150.11	$150.10	$150.10
Purchase #7	$118.65	13.378%	$134.523	$134.52	$134.50	$134.50
7 purchase totals =	$834.08		$915.1386	$915.13	$915.10	$915.10