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 $230.55   13.343%   $261.3123   $261.31   $261.30   $261.30  
  Purchase #2 $46.41   11.412%   $51.7063   $51.71   $51.70   $51.70  
  Purchase #3 $53.87   8.806%   $58.6138   $58.61   $58.60   $58.60  
  Purchase #4 $227.62   6.726%   $242.9297   $242.93   $242.95   $242.90  
  Purchase #5 $203.76   4.289%   $212.4993   $212.50   $212.50   $212.50  
  Purchase #6 $213.43   6.168%   $226.5944   $226.59   $226.60   $226.60  
  Purchase #7 $44.34   10.582%   $49.0321   $49.03   $49.05   $49.00  
  7 purchase totals = $1,019.98       $1,102.6879   $1,102.68   $1,102.70   $1,102.60