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	$199.98	11.358%	$222.6937	$222.69	$222.70	$222.70
Purchase #2	$144.62	7.721%	$155.7861	$155.79	$155.80	$155.80
Purchase #3	$57.80	11.779%	$64.6083	$64.61	$64.60	$64.60
Purchase #4	$6.76	12.231%	$7.5868	$7.59	$7.60	$7.60
Purchase #5	$116.32	10.472%	$128.501	$128.50	$128.50	$128.50
Purchase #6	$77.65	7.713%	$83.6391	$83.64	$83.65	$83.60
Purchase #7	$48.79	4.544%	$51.007	$51.01	$51.00	$51.00
7 purchase totals =	$651.92		$713.8220	$713.83	$713.85	$713.80