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 $247.78   8.124%   $267.9096   $267.91   $267.90   $267.90  
  Purchase #2 $213.36   7.699%   $229.7866   $229.79   $229.80   $229.80  
  Purchase #3 $88.93   10.202%   $98.0026   $98.00   $98.00   $98.00  
  Purchase #4 $59.78   4.817%   $62.6596   $62.66   $62.65   $62.70  
  Purchase #5 $61.63   13.298%   $69.8256   $69.83   $69.85   $69.80  
  Purchase #6 $163.32   5.775%   $172.7517   $172.75   $172.75   $172.80  
  Purchase #7 $115.90   7.457%   $124.5427   $124.54   $124.55   $124.50  
  7 purchase totals = $950.70       $1,025.4784   $1,025.48   $1,025.50   $1,025.50