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 $56.59   11.736%   $63.2314   $63.23   $63.25   $63.20  
  Purchase #2 $13.85   8.726%   $15.0586   $15.06   $15.05   $15.10  
  Purchase #3 $177.68   12.121%   $199.2166   $199.22   $199.20   $199.20  
  Purchase #4 $85.70   9.626%   $93.9495   $93.95   $93.95   $93.90  
  Purchase #5 $188.86   13.517%   $214.3882   $214.39   $214.40   $214.40  
  Purchase #6 $235.42   12.723%   $265.3725   $265.37   $265.35   $265.40  
  Purchase #7 $108.34   12.642%   $122.0363   $122.04   $122.05   $122.00  
  7 purchase totals = $866.44       $973.2531   $973.26   $973.25   $973.20