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 $186.61   11.795%   $208.6206   $208.62   $208.60   $208.60  
  Purchase #2 $32.56   12.464%   $36.6183   $36.62   $36.60   $36.60  
  Purchase #3 $68.50   6.727%   $73.108   $73.11   $73.10   $73.10  
  Purchase #4 $88.47   11.669%   $98.7936   $98.79   $98.80   $98.80  
  Purchase #5 $51.66   7.373%   $55.4689   $55.47   $55.45   $55.50  
  Purchase #6 $106.81   13.737%   $121.4825   $121.48   $121.50   $121.50  
  Purchase #7 $20.56   10.145%   $22.6458   $22.65   $22.65   $22.60  
  7 purchase totals = $555.17       $616.7377   $616.74   $616.70   $616.70