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 $55.77   8.637%   $60.5869   $60.59   $60.60   $60.60  
  Purchase #2 $249.70   4.109%   $259.9602   $259.96   $259.95   $260.00  
  Purchase #3 $73.91   8.518%   $80.2057   $80.21   $80.20   $80.20  
  Purchase #4 $95.57   7.720%   $102.948   $102.95   $102.95   $102.90  
  Purchase #5 $138.27   12.287%   $155.2592   $155.26   $155.25   $155.30  
  Purchase #6 $73.43   9.244%   $80.2179   $80.22   $80.20   $80.20  
  Purchase #7 $28.93   13.124%   $32.7268   $32.73   $32.75   $32.70  
  7 purchase totals = $715.58       $771.9047   $771.92   $771.90   $771.90