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	$120.34	6.161%	$127.7541	$127.75	$127.75	$127.80
Purchase #2	$216.80	6.580%	$231.0654	$231.07	$231.05	$231.10
Purchase #3	$100.46	9.343%	$109.846	$109.85	$109.85	$109.80
Purchase #4	$247.96	12.622%	$279.2575	$279.26	$279.25	$279.30
Purchase #5	$72.41	13.315%	$82.0514	$82.05	$82.05	$82.10
Purchase #6	$41.63	4.694%	$43.5841	$43.58	$43.60	$43.60
Purchase #7	$182.65	3.190%	$188.4765	$188.48	$188.50	$188.50
7 purchase totals =	$982.25		$1,062.0350	$1,062.04	$1,062.05	$1,062.20