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 $70.50   12.398%   $79.2406   $79.24   $79.25   $79.20  
  Purchase #2 $176.94   9.415%   $193.5989   $193.60   $193.60   $193.60  
  Purchase #3 $76.84   13.300%   $87.0597   $87.06   $87.05   $87.10  
  Purchase #4 $220.77   13.265%   $250.0551   $250.06   $250.05   $250.10  
  Purchase #5 $207.38   4.594%   $216.907   $216.91   $216.90   $216.90  
  Purchase #6 $93.93   11.475%   $104.7085   $104.71   $104.70   $104.70  
  Purchase #7 $70.69   6.276%   $75.1265   $75.13   $75.15   $75.10  
  7 purchase totals = $917.05       $1,006.6963   $1,006.71   $1,006.70   $1,006.70