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 $112.25   7.445%   $120.607   $120.61   $120.60   $120.60  
  Purchase #2 $115.56   8.676%   $125.586   $125.59   $125.60   $125.60  
  Purchase #3 $182.53   7.347%   $195.9405   $195.94   $195.95   $195.90  
  Purchase #4 $87.79   4.115%   $91.4026   $91.40   $91.40   $91.40  
  Purchase #5 $105.80   11.786%   $118.2696   $118.27   $118.25   $118.30  
  Purchase #6 $8.91   4.544%   $9.3149   $9.31   $9.30   $9.30  
  Purchase #7 $40.97   7.109%   $43.8826   $43.88   $43.90   $43.90  
  7 purchase totals = $653.81       $705.0032   $705.00   $705.00   $705.00