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 $163.69   13.659%   $186.0484   $186.05   $186.05   $186.00  
  Purchase #2 $239.32   4.693%   $250.5513   $250.55   $250.55   $250.60  
  Purchase #3 $55.28   7.120%   $59.2159   $59.22   $59.20   $59.20  
  Purchase #4 $227.49   6.652%   $242.6226   $242.62   $242.60   $242.60  
  Purchase #5 $51.73   5.289%   $54.466   $54.47   $54.45   $54.50  
  Purchase #6 $74.36   13.412%   $84.3332   $84.33   $84.35   $84.30  
  Purchase #7 $191.93   5.152%   $201.8182   $201.82   $201.80   $201.80  
  7 purchase totals = $1,003.80       $1,079.0556   $1,079.06   $1,079.00   $1,079.00