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 $119.57   5.213%   $125.8032   $125.80   $125.80   $125.80  
  Purchase #2 $41.84   9.232%   $45.7027   $45.70   $45.70   $45.70  
  Purchase #3 $222.70   9.848%   $244.6315   $244.63   $244.65   $244.60  
  Purchase #4 $46.84   12.727%   $52.8013   $52.80   $52.80   $52.80  
  Purchase #5 $88.39   12.466%   $99.4087   $99.41   $99.40   $99.40  
  Purchase #6 $235.26   10.684%   $260.3952   $260.40   $260.40   $260.40  
  Purchase #7 $60.68   13.745%   $69.0205   $69.02   $69.00   $69.00  
  7 purchase totals = $815.28       $897.7631   $897.76   $897.75   $897.70