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 $250.50   6.692%   $267.2635   $267.26   $267.25   $267.30  
  Purchase #2 $89.43   10.376%   $98.7093   $98.71   $98.70   $98.70  
  Purchase #3 $54.94   13.801%   $62.5223   $62.52   $62.50   $62.50  
  Purchase #4 $216.61   7.213%   $232.2341   $232.23   $232.25   $232.20  
  Purchase #5 $208.28   8.838%   $226.6878   $226.69   $226.70   $226.70  
  Purchase #6 $130.41   12.167%   $146.277   $146.28   $146.30   $146.30  
  Purchase #7 $44.72   12.192%   $50.1723   $50.17   $50.15   $50.20  
  7 purchase totals = $994.89       $1,083.8663   $1,083.86   $1,083.85   $1,083.90