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 $58.60   5.812%   $62.0058   $62.01   $62.00   $62.00  
  Purchase #2 $114.49   12.543%   $128.8505   $128.85   $128.85   $128.90  
  Purchase #3 $141.57   8.508%   $153.6148   $153.61   $153.60   $153.60  
  Purchase #4 $26.81   11.624%   $29.9264   $29.93   $29.95   $29.90  
  Purchase #5 $143.64   12.652%   $161.8133   $161.81   $161.80   $161.80  
  Purchase #6 $130.43   11.121%   $144.9351   $144.94   $144.95   $144.90  
  Purchase #7 $225.27   8.202%   $243.7466   $243.75   $243.75   $243.70  
  7 purchase totals = $840.81       $924.8925   $924.90   $924.90   $924.80