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 $158.63   10.509%   $175.3004   $175.30   $175.30   $175.30  
  Purchase #2 $196.48   13.307%   $222.6256   $222.63   $222.65   $222.60  
  Purchase #3 $66.75   5.627%   $70.506   $70.51   $70.50   $70.50  
  Purchase #4 $118.79   4.870%   $124.5751   $124.58   $124.60   $124.60  
  Purchase #5 $216.37   13.210%   $244.9525   $244.95   $244.95   $245.00  
  Purchase #6 $48.76   13.291%   $55.2407   $55.24   $55.25   $55.20  
  Purchase #7 $153.47   10.801%   $170.0463   $170.05   $170.05   $170.00  
  7 purchase totals = $959.25       $1,063.2466   $1,063.26   $1,063.30   $1,063.20