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	$154.59	12.858%	$174.4672	$174.47	$174.45	$174.50
Purchase #2	$90.71	5.329%	$95.5439	$95.54	$95.55	$95.50
Purchase #3	$93.76	8.149%	$101.4005	$101.40	$101.40	$101.40
Purchase #4	$57.55	7.400%	$61.8087	$61.81	$61.80	$61.80
Purchase #5	$156.80	5.127%	$164.8391	$164.84	$164.85	$164.80
Purchase #6	$72.60	11.711%	$81.1022	$81.10	$81.10	$81.10
Purchase #7	$82.50	11.750%	$92.1938	$92.19	$92.20	$92.20
7 purchase totals =	$708.51		$771.3554	$771.35	$771.35	$771.30