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 $239.47   12.529%   $269.4732   $269.47   $269.45   $269.50  
  Purchase #2 $43.69   5.204%   $45.9636   $45.96   $45.95   $46.00  
  Purchase #3 $246.49   13.821%   $280.5574   $280.56   $280.55   $280.60  
  Purchase #4 $177.87   5.676%   $187.9659   $187.97   $187.95   $188.00  
  Purchase #5 $31.56   4.360%   $32.936   $32.94   $32.95   $32.90  
  Purchase #6 $101.69   7.759%   $109.5801   $109.58   $109.60   $109.60  
  Purchase #7 $24.87   5.332%   $26.1961   $26.20   $26.20   $26.20  
  7 purchase totals = $865.64       $952.6723   $952.68   $952.65   $952.80