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	$105.66	6.462%	$112.4877	$112.49	$112.50	$112.50
Purchase #2	$92.91	11.503%	$103.5974	$103.60	$103.60	$103.60
Purchase #3	$37.54	11.439%	$41.8342	$41.83	$41.85	$41.80
Purchase #4	$18.95	7.306%	$20.3345	$20.33	$20.35	$20.30
Purchase #5	$243.68	6.425%	$259.3364	$259.34	$259.35	$259.30
Purchase #6	$124.29	12.344%	$139.6324	$139.63	$139.65	$139.60
Purchase #7	$233.30	12.300%	$261.9959	$262.00	$262.00	$262.00
7 purchase totals =	$856.33		$939.2185	$939.22	$939.30	$939.10