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	$109.33	11.461%	$121.8603	$121.86	$121.85	$121.90
Purchase #2	$93.70	12.455%	$105.3703	$105.37	$105.35	$105.40
Purchase #3	$46.76	3.566%	$48.4275	$48.43	$48.45	$48.40
Purchase #4	$82.87	3.735%	$85.9652	$85.97	$85.95	$86.00
Purchase #5	$94.80	7.403%	$101.818	$101.82	$101.80	$101.80
Purchase #6	$5.80	12.570%	$6.5291	$6.53	$6.55	$6.50
Purchase #7	$34.61	7.697%	$37.2739	$37.27	$37.25	$37.30
7 purchase totals =	$467.87		$507.2443	$507.25	$507.20	$507.30