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 $115.63   6.332%   $122.9517   $122.95   $122.95   $123.00  
  Purchase #2 $243.28   6.541%   $259.1929   $259.19   $259.20   $259.20  
  Purchase #3 $37.78   5.870%   $39.9977   $40.00   $40.00   $40.00  
  Purchase #4 $114.97   7.282%   $123.3421   $123.34   $123.35   $123.30  
  Purchase #5 $211.75   8.609%   $229.9796   $229.98   $230.00   $230.00  
  Purchase #6 $55.67   5.418%   $58.6862   $58.69   $58.70   $58.70  
  Purchase #7 $214.71   12.665%   $241.903   $241.90   $241.90   $241.90  
  7 purchase totals = $993.79       $1,076.0532   $1,076.05   $1,076.10   $1,076.10