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 $174.92   10.387%   $193.0889   $193.09   $193.10   $193.10  
  Purchase #2 $246.36   5.293%   $259.3998   $259.40   $259.40   $259.40  
  Purchase #3 $104.87   4.827%   $109.9321   $109.93   $109.95   $109.90  
  Purchase #4 $165.45   9.230%   $180.721   $180.72   $180.70   $180.70  
  Purchase #5 $208.87   7.568%   $224.6773   $224.68   $224.70   $224.70  
  Purchase #6 $212.98   4.729%   $223.0518   $223.05   $223.05   $223.10  
  Purchase #7 $58.30   5.587%   $61.5572   $61.56   $61.55   $61.60  
  7 purchase totals = $1,171.75       $1,252.4281   $1,252.43   $1,252.45   $1,252.50