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 $82.94   11.778%   $92.7087   $92.71   $92.70   $92.70  
  Purchase #2 $196.32   3.212%   $202.6258   $202.63   $202.65   $202.60  
  Purchase #3 $19.71   3.431%   $20.3863   $20.39   $20.40   $20.40  
  Purchase #4 $184.58   6.820%   $197.1684   $197.17   $197.15   $197.20  
  Purchase #5 $59.66   12.187%   $66.9308   $66.93   $66.95   $66.90  
  Purchase #6 $230.84   7.816%   $248.8825   $248.88   $248.90   $248.90  
  Purchase #7 $145.87   6.119%   $154.7958   $154.80   $154.80   $154.80  
  7 purchase totals = $919.92       $983.4983   $983.51   $983.55   $983.50