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 $166.47   7.802%   $179.458   $179.46   $179.45   $179.50  
  Purchase #2 $209.57   8.149%   $226.6479   $226.65   $226.65   $226.60  
  Purchase #3 $61.36   13.513%   $69.6516   $69.65   $69.65   $69.70  
  Purchase #4 $162.83   7.806%   $175.5405   $175.54   $175.55   $175.50  
  Purchase #5 $174.99   12.240%   $196.4088   $196.41   $196.40   $196.40  
  Purchase #6 $31.92   12.626%   $35.9502   $35.95   $35.95   $36.00  
  Purchase #7 $217.71   9.423%   $238.2248   $238.22   $238.20   $238.20  
  7 purchase totals = $1,024.85       $1,121.8818   $1,121.88   $1,121.85   $1,121.90