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	$207.45	5.329%	$218.505	$218.51	$218.50	$218.50
Purchase #2	$234.46	6.811%	$250.4291	$250.43	$250.45	$250.40
Purchase #3	$83.28	5.704%	$88.0303	$88.03	$88.05	$88.00
Purchase #4	$45.26	12.440%	$50.8903	$50.89	$50.90	$50.90
Purchase #5	$248.25	12.437%	$279.1249	$279.12	$279.10	$279.10
Purchase #6	$41.32	9.596%	$45.2851	$45.29	$45.30	$45.30
Purchase #7	$118.34	8.697%	$128.632	$128.63	$128.65	$128.60
7 purchase totals =	$978.36		$1,060.8967	$1,060.90	$1,060.95	$1,060.80