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	$17.82	6.382%	$18.9573	$18.96	$18.95	$19.00
Purchase #2	$249.28	8.830%	$271.2914	$271.29	$271.30	$271.30
Purchase #3	$90.97	11.813%	$101.7163	$101.72	$101.70	$101.70
Purchase #4	$78.57	4.230%	$81.8935	$81.89	$81.90	$81.90
Purchase #5	$82.37	8.710%	$89.5444	$89.54	$89.55	$89.50
Purchase #6	$56.96	11.218%	$63.3498	$63.35	$63.35	$63.30
Purchase #7	$22.97	12.387%	$25.8153	$25.82	$25.80	$25.80
7 purchase totals =	$598.94		$652.5680	$652.57	$652.55	$652.50