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 $244.58   6.419%   $260.2796   $260.28   $260.30   $260.30  
  Purchase #2 $25.76   7.503%   $27.6928   $27.69   $27.70   $27.70  
  Purchase #3 $125.51   10.119%   $138.2104   $138.21   $138.20   $138.20  
  Purchase #4 $158.80   6.381%   $168.933   $168.93   $168.95   $168.90  
  Purchase #5 $31.47   12.518%   $35.4094   $35.41   $35.40   $35.40  
  Purchase #6 $94.38   9.659%   $103.4962   $103.50   $103.50   $103.50  
  Purchase #7 $23.88   5.603%   $25.218   $25.22   $25.20   $25.20  
  7 purchase totals = $704.38       $759.2394   $759.24   $759.25   $759.20