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 $238.99   9.519%   $261.7395   $261.74   $261.75   $261.70  
  Purchase #2 $196.54   11.700%   $219.5352   $219.54   $219.55   $219.50  
  Purchase #3 $136.98   5.464%   $144.4646   $144.46   $144.45   $144.50  
  Purchase #4 $234.82   12.500%   $264.1725   $264.17   $264.15   $264.20  
  Purchase #5 $106.33   6.757%   $113.5147   $113.51   $113.50   $113.50  
  Purchase #6 $186.90   5.492%   $197.1645   $197.16   $197.15   $197.20  
  Purchase #7 $150.99   13.362%   $171.1653   $171.17   $171.15   $171.20  
  7 purchase totals = $1,251.55       $1,371.7563   $1,371.75   $1,371.70   $1,371.80