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 $58.89   12.652%   $66.3408   $66.34   $66.35   $66.30  
  Purchase #2 $49.28   8.482%   $53.4599   $53.46   $53.45   $53.50  
  Purchase #3 $131.62   8.682%   $143.0472   $143.05   $143.05   $143.00  
  Purchase #4 $240.91   8.500%   $261.3874   $261.39   $261.40   $261.40  
  Purchase #5 $58.45   5.818%   $61.8506   $61.85   $61.85   $61.90  
  Purchase #6 $185.78   9.500%   $203.4291   $203.43   $203.45   $203.40  
  Purchase #7 $37.44   4.418%   $39.0941   $39.09   $39.10   $39.10  
  7 purchase totals = $762.37       $828.6091   $828.61   $828.65   $828.60