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	$134.85	5.159%	$141.8069	$141.81	$141.80	$141.80
Purchase #2	$53.95	5.670%	$57.009	$57.01	$57.00	$57.00
Purchase #3	$133.94	12.397%	$150.5445	$150.54	$150.55	$150.50
Purchase #4	$136.41	10.519%	$150.759	$150.76	$150.75	$150.80
Purchase #5	$204.48	9.801%	$224.5211	$224.52	$224.50	$224.50
Purchase #6	$132.54	5.867%	$140.3161	$140.32	$140.30	$140.30
Purchase #7	$122.77	7.490%	$131.9655	$131.97	$131.95	$132.00
7 purchase totals =	$918.94		$996.9221	$996.93	$996.85	$996.90