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 $119.27   13.156%   $134.9612   $134.96   $134.95   $135.00  
  Purchase #2 $95.70   7.397%   $102.7789   $102.78   $102.80   $102.80  
  Purchase #3 $184.75   6.458%   $196.6812   $196.68   $196.70   $196.70  
  Purchase #4 $118.76   3.525%   $122.9463   $122.95   $122.95   $122.90  
  Purchase #5 $217.60   10.494%   $240.4349   $240.43   $240.45   $240.40  
  Purchase #6 $65.88   10.203%   $72.6017   $72.60   $72.60   $72.60  
  Purchase #7 $21.70   3.475%   $22.4541   $22.45   $22.45   $22.50  
  7 purchase totals = $823.66       $892.8583   $892.85   $892.90   $892.90