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	$18.40	8.462%	$19.957	$19.96	$19.95	$20.00
Purchase #2	$228.46	12.557%	$257.1477	$257.15	$257.15	$257.10
Purchase #3	$78.34	9.494%	$85.7776	$85.78	$85.80	$85.80
Purchase #4	$89.46	3.416%	$92.516	$92.52	$92.50	$92.50
Purchase #5	$234.57	12.676%	$264.3041	$264.30	$264.30	$264.30
Purchase #6	$168.29	10.684%	$186.2701	$186.27	$186.25	$186.30
Purchase #7	$133.52	8.484%	$144.8478	$144.85	$144.85	$144.80
7 purchase totals =	$951.04		$1,050.8203	$1,050.83	$1,050.80	$1,050.80