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 $24.64   9.728%   $27.037   $27.04   $27.05   $27.00  
  Purchase #2 $119.25   10.670%   $131.974   $131.97   $131.95   $132.00  
  Purchase #3 $183.49   4.570%   $191.8755   $191.88   $191.90   $191.90  
  Purchase #4 $180.93   4.805%   $189.6237   $189.62   $189.60   $189.60  
  Purchase #5 $131.44   5.267%   $138.3629   $138.36   $138.35   $138.40  
  Purchase #6 $182.49   8.736%   $198.4323   $198.43   $198.45   $198.40  
  Purchase #7 $132.84   10.190%   $146.3764   $146.38   $146.40   $146.40  
  7 purchase totals = $955.08       $1,023.6818   $1,023.68   $1,023.70   $1,023.70