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 $104.81   13.787%   $119.2602   $119.26   $119.25   $119.30  
  Purchase #2 $106.33   5.177%   $111.8347   $111.83   $111.85   $111.80  
  Purchase #3 $118.88   5.128%   $124.9762   $124.98   $125.00   $125.00  
  Purchase #4 $214.38   4.835%   $224.7453   $224.75   $224.75   $224.70  
  Purchase #5 $118.60   13.115%   $134.1544   $134.15   $134.15   $134.20  
  Purchase #6 $203.62   11.513%   $227.0628   $227.06   $227.05   $227.10  
  Purchase #7 $168.53   3.604%   $174.6038   $174.60   $174.60   $174.60  
  7 purchase totals = $1,035.15       $1,116.6374   $1,116.63   $1,116.65   $1,116.70