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 $84.42   9.659%   $92.5741   $92.57   $92.55   $92.60  
  Purchase #2 $210.87   8.630%   $229.0681   $229.07   $229.05   $229.10  
  Purchase #3 $46.87   8.712%   $50.9533   $50.95   $50.95   $51.00  
  Purchase #4 $136.37   7.581%   $146.7082   $146.71   $146.70   $146.70  
  Purchase #5 $103.57   7.518%   $111.3564   $111.36   $111.35   $111.40  
  Purchase #6 $195.58   7.503%   $210.2544   $210.25   $210.25   $210.30  
  Purchase #7 $217.80   6.532%   $232.0267   $232.03   $232.05   $232.00  
  7 purchase totals = $995.48       $1,072.9412   $1,072.94   $1,072.90   $1,073.10