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 $93.32   12.189%   $104.6948   $104.69   $104.70   $104.70  
  Purchase #2 $180.93   12.545%   $203.6277   $203.63   $203.65   $203.60  
  Purchase #3 $184.47   5.108%   $193.8927   $193.89   $193.90   $193.90  
  Purchase #4 $65.49   8.341%   $70.9525   $70.95   $70.95   $71.00  
  Purchase #5 $194.84   11.391%   $217.0342   $217.03   $217.05   $217.00  
  Purchase #6 $38.78   8.592%   $42.112   $42.11   $42.10   $42.10  
  Purchase #7 $118.96   5.421%   $125.4088   $125.41   $125.40   $125.40  
  7 purchase totals = $876.79       $957.7227   $957.71   $957.75   $957.70