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 $177.25   6.485%   $188.7447   $188.74   $188.75   $188.70  
  Purchase #2 $30.70   12.851%   $34.6453   $34.65   $34.65   $34.60  
  Purchase #3 $208.66   13.631%   $237.1024   $237.10   $237.10   $237.10  
  Purchase #4 $68.79   3.587%   $71.2575   $71.26   $71.25   $71.30  
  Purchase #5 $68.29   12.245%   $76.6521   $76.65   $76.65   $76.70  
  Purchase #6 $24.96   3.121%   $25.739   $25.74   $25.75   $25.70  
  Purchase #7 $245.57   4.874%   $257.5391   $257.54   $257.55   $257.50  
  7 purchase totals = $824.22       $891.6801   $891.68   $891.70   $891.60