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 $52.66   8.546%   $57.1603   $57.16   $57.15   $57.20  
  Purchase #2 $178.33   4.188%   $185.7985   $185.80   $185.80   $185.80  
  Purchase #3 $224.35   11.392%   $249.908   $249.91   $249.90   $249.90  
  Purchase #4 $230.40   12.452%   $259.0894   $259.09   $259.10   $259.10  
  Purchase #5 $39.47   13.237%   $44.6946   $44.69   $44.70   $44.70  
  Purchase #6 $14.42   12.410%   $16.2095   $16.21   $16.20   $16.20  
  Purchase #7 $155.75   3.730%   $161.5595   $161.56   $161.55   $161.60  
  7 purchase totals = $895.38       $974.4198   $974.42   $974.40   $974.50