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 $103.66   8.840%   $112.8235   $112.82   $112.80   $112.80  
  Purchase #2 $226.28   8.321%   $245.1088   $245.11   $245.10   $245.10  
  Purchase #3 $90.28   5.753%   $95.4738   $95.47   $95.45   $95.50  
  Purchase #4 $103.94   3.410%   $107.4844   $107.48   $107.50   $107.50  
  Purchase #5 $14.75   7.186%   $15.8099   $15.81   $15.80   $15.80  
  Purchase #6 $23.51   9.214%   $25.6762   $25.68   $25.70   $25.70  
  Purchase #7 $40.80   4.604%   $42.6784   $42.68   $42.70   $42.70  
  7 purchase totals = $603.22       $645.0550   $645.05   $645.05   $645.10