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 $119.75   12.341%   $134.5283   $134.53   $134.55   $134.50  
  Purchase #2 $85.62   12.674%   $96.4715   $96.47   $96.45   $96.50  
  Purchase #3 $228.95   8.290%   $247.93   $247.93   $247.95   $247.90  
  Purchase #4 $105.85   10.449%   $116.9103   $116.91   $116.90   $116.90  
  Purchase #5 $130.79   5.861%   $138.4556   $138.46   $138.45   $138.50  
  Purchase #6 $177.87   10.439%   $196.4378   $196.44   $196.45   $196.40  
  Purchase #7 $94.42   13.739%   $107.3924   $107.39   $107.40   $107.40  
  7 purchase totals = $943.25       $1,038.1259   $1,038.13   $1,038.15   $1,038.10