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 $110.41   10.822%   $122.3586   $122.36   $122.35   $122.40  
  Purchase #2 $232.95   5.468%   $245.6877   $245.69   $245.70   $245.70  
  Purchase #3 $96.32   9.511%   $105.481   $105.48   $105.50   $105.50  
  Purchase #4 $48.56   10.433%   $53.6263   $53.63   $53.65   $53.60  
  Purchase #5 $120.70   8.786%   $131.3047   $131.30   $131.30   $131.30  
  Purchase #6 $152.44   8.857%   $165.9416   $165.94   $165.95   $165.90  
  Purchase #7 $123.74   10.134%   $136.2798   $136.28   $136.30   $136.30  
  7 purchase totals = $885.12       $960.6797   $960.68   $960.75   $960.70