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 $163.60   11.128%   $181.8054   $181.81   $181.80   $181.80  
  Purchase #2 $142.98   4.604%   $149.5628   $149.56   $149.55   $149.60  
  Purchase #3 $126.73   4.134%   $131.969   $131.97   $131.95   $132.00  
  Purchase #4 $5.76   13.798%   $6.5548   $6.55   $6.55   $6.60  
  Purchase #5 $52.62   6.737%   $56.165   $56.17   $56.15   $56.20  
  Purchase #6 $163.37   6.819%   $174.5102   $174.51   $174.50   $174.50  
  Purchase #7 $250.41   9.815%   $274.9877   $274.99   $275.00   $275.00  
  7 purchase totals = $905.47       $975.5549   $975.56   $975.50   $975.70