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 $182.95   11.262%   $203.5538   $203.55   $203.55   $203.60  
  Purchase #2 $201.38   11.832%   $225.2073   $225.21   $225.20   $225.20  
  Purchase #3 $239.63   4.509%   $250.4349   $250.43   $250.45   $250.40  
  Purchase #4 $133.26   12.344%   $149.7096   $149.71   $149.70   $149.70  
  Purchase #5 $118.36   13.547%   $134.3942   $134.39   $134.40   $134.40  
  Purchase #6 $22.33   11.835%   $24.9728   $24.97   $24.95   $25.00  
  Purchase #7 $27.95   13.460%   $31.7121   $31.71   $31.70   $31.70  
  7 purchase totals = $925.86       $1,019.9847   $1,019.97   $1,019.95   $1,020.00