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 $208.83   8.155%   $225.8601   $225.86   $225.85   $225.90  
  Purchase #2 $51.90   10.678%   $57.4419   $57.44   $57.45   $57.40  
  Purchase #3 $10.68   4.782%   $11.1907   $11.19   $11.20   $11.20  
  Purchase #4 $92.42   11.531%   $103.077   $103.08   $103.10   $103.10  
  Purchase #5 $210.81   10.402%   $232.7385   $232.74   $232.75   $232.70  
  Purchase #6 $208.43   8.175%   $225.4692   $225.47   $225.45   $225.50  
  Purchase #7 $126.81   8.611%   $137.7296   $137.73   $137.75   $137.70  
  7 purchase totals = $909.88       $993.5070   $993.51   $993.55   $993.50