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	$123.77	6.820%	$132.2111	$132.21	$132.20	$132.20
Purchase #2	$148.90	5.586%	$157.2176	$157.22	$157.20	$157.20
Purchase #3	$115.66	13.409%	$131.1688	$131.17	$131.15	$131.20
Purchase #4	$60.25	10.520%	$66.5883	$66.59	$66.60	$66.60
Purchase #5	$164.59	9.826%	$180.7626	$180.76	$180.75	$180.80
Purchase #6	$97.36	8.700%	$105.8303	$105.83	$105.85	$105.80
Purchase #7	$182.77	7.364%	$196.2292	$196.23	$196.25	$196.20
7 purchase totals =	$893.30		$970.0079	$970.01	$970.00	$970.00