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 $65.63   13.102%   $74.2288   $74.23   $74.25   $74.20  
  Purchase #2 $148.87   8.264%   $161.1726   $161.17   $161.15   $161.20  
  Purchase #3 $239.95   3.766%   $248.9865   $248.99   $249.00   $249.00  
  Purchase #4 $89.35   4.569%   $93.4324   $93.43   $93.45   $93.40  
  Purchase #5 $79.67   10.836%   $88.303   $88.30   $88.30   $88.30  
  Purchase #6 $214.88   11.560%   $239.7201   $239.72   $239.70   $239.70  
  Purchase #7 $89.81   11.588%   $100.2172   $100.22   $100.20   $100.20  
  7 purchase totals = $928.16       $1,006.0606   $1,006.06   $1,006.05   $1,006.00