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 $50.27   11.383%   $55.9922   $55.99   $56.00   $56.00  
  Purchase #2 $230.81   11.546%   $257.4593   $257.46   $257.45   $257.50  
  Purchase #3 $221.96   6.499%   $236.3852   $236.39   $236.40   $236.40  
  Purchase #4 $69.27   12.214%   $77.7306   $77.73   $77.75   $77.70  
  Purchase #5 $172.84   4.698%   $180.96   $180.96   $180.95   $181.00  
  Purchase #6 $184.94   12.176%   $207.4583   $207.46   $207.45   $207.50  
  Purchase #7 $5.42   10.439%   $5.9858   $5.99   $6.00   $6.00  
  7 purchase totals = $935.51       $1,021.9714   $1,021.98   $1,022.00   $1,022.10