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 $160.60   13.653%   $182.5267   $182.53   $182.55   $182.50  
  Purchase #2 $37.95   11.120%   $42.17   $42.17   $42.15   $42.20  
  Purchase #3 $241.28   7.231%   $258.727   $258.73   $258.75   $258.70  
  Purchase #4 $105.33   7.481%   $113.2097   $113.21   $113.20   $113.20  
  Purchase #5 $173.76   11.569%   $193.8623   $193.86   $193.85   $193.90  
  Purchase #6 $16.27   8.608%   $17.6705   $17.67   $17.65   $17.70  
  Purchase #7 $249.60   7.410%   $268.0954   $268.10   $268.10   $268.10  
  7 purchase totals = $984.79       $1,076.2616   $1,076.27   $1,076.25   $1,076.30