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	$99.51	12.835%	$112.2821	$112.28	$112.30	$112.30
Purchase #2	$38.93	12.591%	$43.8317	$43.83	$43.85	$43.80
Purchase #3	$77.63	11.131%	$86.271	$86.27	$86.25	$86.30
Purchase #4	$118.52	7.650%	$127.5868	$127.59	$127.60	$127.60
Purchase #5	$144.67	3.736%	$150.0749	$150.07	$150.05	$150.10
Purchase #6	$248.47	5.135%	$261.2289	$261.23	$261.25	$261.20
Purchase #7	$17.26	4.669%	$18.0659	$18.07	$18.05	$18.10
7 purchase totals =	$744.99		$799.3413	$799.34	$799.35	$799.40