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 $69.90   4.652%   $73.1517   $73.15   $73.15   $73.20  
  Purchase #2 $212.29   13.456%   $240.8557   $240.86   $240.85   $240.90  
  Purchase #3 $242.95   6.462%   $258.6494   $258.65   $258.65   $258.60  
  Purchase #4 $42.74   9.241%   $46.6896   $46.69   $46.70   $46.70  
  Purchase #5 $58.74   13.871%   $66.8878   $66.89   $66.90   $66.90  
  Purchase #6 $227.76   4.554%   $238.1322   $238.13   $238.15   $238.10  
  Purchase #7 $227.96   13.527%   $258.7961   $258.80   $258.80   $258.80  
  7 purchase totals = $1,082.34       $1,183.1625   $1,183.17   $1,183.20   $1,183.20