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 $76.98   8.290%   $83.3616   $83.36   $83.35   $83.40  
  Purchase #2 $177.72   5.749%   $187.9371   $187.94   $187.95   $187.90  
  Purchase #3 $122.93   9.721%   $134.88   $134.88   $134.90   $134.90  
  Purchase #4 $192.61   4.102%   $200.5109   $200.51   $200.50   $200.50  
  Purchase #5 $84.92   8.353%   $92.0134   $92.01   $92.00   $92.00  
  Purchase #6 $232.67   4.360%   $242.8144   $242.81   $242.80   $242.80  
  Purchase #7 $5.86   3.370%   $6.0575   $6.06   $6.05   $6.10  
  7 purchase totals = $893.69       $947.5749   $947.57   $947.55   $947.60