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 $53.60   12.551%   $60.3273   $60.33   $60.35   $60.30  
  Purchase #2 $23.55   8.796%   $25.6215   $25.62   $25.60   $25.60  
  Purchase #3 $250.67   8.309%   $271.4982   $271.50   $271.50   $271.50  
  Purchase #4 $17.94   6.278%   $19.0663   $19.07   $19.05   $19.10  
  Purchase #5 $201.75   3.514%   $208.8395   $208.84   $208.85   $208.80  
  Purchase #6 $223.36   13.473%   $253.4533   $253.45   $253.45   $253.50  
  Purchase #7 $164.72   7.273%   $176.7001   $176.70   $176.70   $176.70  
  7 purchase totals = $935.59       $1,015.5062   $1,015.51   $1,015.50   $1,015.50