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 $203.65   11.782%   $227.644   $227.64   $227.65   $227.60  
  Purchase #2 $247.88   5.373%   $261.1986   $261.20   $261.20   $261.20  
  Purchase #3 $8.61   13.382%   $9.7622   $9.76   $9.75   $9.80  
  Purchase #4 $87.76   9.522%   $96.1165   $96.12   $96.10   $96.10  
  Purchase #5 $94.59   8.364%   $102.5015   $102.50   $102.50   $102.50  
  Purchase #6 $233.65   12.793%   $263.5408   $263.54   $263.55   $263.50  
  Purchase #7 $227.68   5.327%   $239.8085   $239.81   $239.80   $239.80  
  7 purchase totals = $1,103.82       $1,200.5721   $1,200.57   $1,200.55   $1,200.50