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 $238.69   12.211%   $267.8364   $267.84   $267.85   $267.80  
  Purchase #2 $93.36   10.190%   $102.8734   $102.87   $102.85   $102.90  
  Purchase #3 $6.65   6.335%   $7.0713   $7.07   $7.05   $7.10  
  Purchase #4 $146.98   3.343%   $151.8935   $151.89   $151.90   $151.90  
  Purchase #5 $176.99   12.358%   $198.8624   $198.86   $198.85   $198.90  
  Purchase #6 $25.31   4.144%   $26.3588   $26.36   $26.35   $26.40  
  Purchase #7 $174.93   8.140%   $189.1693   $189.17   $189.15   $189.20  
  7 purchase totals = $862.91       $944.0651   $944.06   $944.00   $944.20