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 $14.92   8.154%   $16.1366   $16.14   $16.15   $16.10  
  Purchase #2 $216.97   5.183%   $228.2156   $228.22   $228.20   $228.20  
  Purchase #3 $160.58   12.762%   $181.0732   $181.07   $181.05   $181.10  
  Purchase #4 $127.91   6.536%   $136.2702   $136.27   $136.25   $136.30  
  Purchase #5 $31.99   11.645%   $35.7152   $35.72   $35.70   $35.70  
  Purchase #6 $226.31   9.311%   $247.3817   $247.38   $247.40   $247.40  
  Purchase #7 $131.76   13.344%   $149.3421   $149.34   $149.35   $149.30  
  7 purchase totals = $910.44       $994.1346   $994.14   $994.10   $994.10