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 $41.27   13.284%   $46.7523   $46.75   $46.75   $46.80  
  Purchase #2 $107.38   12.423%   $120.7198   $120.72   $120.70   $120.70  
  Purchase #3 $8.55   7.483%   $9.1898   $9.19   $9.20   $9.20  
  Purchase #4 $38.30   6.770%   $40.8929   $40.89   $40.90   $40.90  
  Purchase #5 $24.60   4.126%   $25.615   $25.62   $25.60   $25.60  
  Purchase #6 $246.38   3.699%   $255.4936   $255.49   $255.50   $255.50  
  Purchase #7 $210.49   13.421%   $238.7399   $238.74   $238.75   $238.70  
  7 purchase totals = $676.97       $737.4033   $737.40   $737.40   $737.40