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 $56.27   11.413%   $62.6921   $62.69   $62.70   $62.70  
  Purchase #2 $9.91   10.798%   $10.9801   $10.98   $11.00   $11.00  
  Purchase #3 $185.73   6.743%   $198.2538   $198.25   $198.25   $198.30  
  Purchase #4 $190.47   10.492%   $210.4541   $210.45   $210.45   $210.50  
  Purchase #5 $74.55   5.574%   $78.7054   $78.71   $78.70   $78.70  
  Purchase #6 $137.97   11.430%   $153.74   $153.74   $153.75   $153.70  
  Purchase #7 $103.35   6.825%   $110.4036   $110.40   $110.40   $110.40  
  7 purchase totals = $758.25       $825.2291   $825.22   $825.25   $825.30