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	$29.40	13.378%	$33.3331	$33.33	$33.35	$33.30
Purchase #2	$108.96	13.136%	$123.273	$123.27	$123.25	$123.30
Purchase #3	$164.34	11.265%	$182.8529	$182.85	$182.85	$182.90
Purchase #4	$219.96	13.561%	$249.7888	$249.79	$249.80	$249.80
Purchase #5	$25.66	5.569%	$27.089	$27.09	$27.10	$27.10
Purchase #6	$95.91	10.436%	$105.9192	$105.92	$105.90	$105.90
Purchase #7	$90.26	3.300%	$93.2386	$93.24	$93.25	$93.20
7 purchase totals =	$734.49		$815.4946	$815.49	$815.50	$815.50