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	$19.63	10.515%	$21.6941	$21.69	$21.70	$21.70
Purchase #2	$240.97	6.412%	$256.421	$256.42	$256.40	$256.40
Purchase #3	$214.81	4.508%	$224.4936	$224.49	$224.50	$224.50
Purchase #4	$223.32	8.290%	$241.8332	$241.83	$241.85	$241.80
Purchase #5	$73.37	6.730%	$78.3078	$78.31	$78.30	$78.30
Purchase #6	$79.66	6.843%	$85.1111	$85.11	$85.10	$85.10
Purchase #7	$65.89	4.609%	$68.9269	$68.93	$68.95	$68.90
7 purchase totals =	$917.65		$976.7877	$976.78	$976.80	$976.70