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	$30.59	12.779%	$34.4991	$34.50	$34.50	$34.50
Purchase #2	$101.30	11.730%	$113.1825	$113.18	$113.20	$113.20
Purchase #3	$166.44	12.544%	$187.3182	$187.32	$187.30	$187.30
Purchase #4	$41.58	5.296%	$43.7821	$43.78	$43.80	$43.80
Purchase #5	$61.85	4.277%	$64.4953	$64.50	$64.50	$64.50
Purchase #6	$39.46	5.321%	$41.5597	$41.56	$41.55	$41.60
Purchase #7	$101.80	3.624%	$105.4892	$105.49	$105.50	$105.50
7 purchase totals =	$543.02		$590.3261	$590.33	$590.35	$590.40