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	$37.96	13.215%	$42.9764	$42.98	$43.00	$43.00
Purchase #2	$150.69	6.858%	$161.0243	$161.02	$161.00	$161.00
Purchase #3	$128.89	7.874%	$139.0388	$139.04	$139.05	$139.00
Purchase #4	$13.89	4.550%	$14.522	$14.52	$14.50	$14.50
Purchase #5	$155.53	6.863%	$166.204	$166.20	$166.20	$166.20
Purchase #6	$144.59	12.488%	$162.6464	$162.65	$162.65	$162.60
Purchase #7	$82.34	3.269%	$85.0317	$85.03	$85.05	$85.00
7 purchase totals =	$713.89		$771.4436	$771.44	$771.45	$771.30