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 $63.89   12.523%   $71.8909   $71.89   $71.90   $71.90  
  Purchase #2 $82.41   4.394%   $86.0311   $86.03   $86.05   $86.00  
  Purchase #3 $114.95   8.590%   $124.8242   $124.82   $124.80   $124.80  
  Purchase #4 $22.87   8.285%   $24.7648   $24.76   $24.75   $24.80  
  Purchase #5 $250.95   4.603%   $262.5012   $262.50   $262.50   $262.50  
  Purchase #6 $203.74   6.617%   $217.2215   $217.22   $217.20   $217.20  
  Purchase #7 $174.56   3.627%   $180.8913   $180.89   $180.90   $180.90  
  7 purchase totals = $913.37       $968.1250   $968.11   $968.10   $968.10