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 $57.86   5.761%   $61.1933   $61.19   $61.20   $61.20  
  Purchase #2 $147.56   7.189%   $158.1681   $158.17   $158.15   $158.20  
  Purchase #3 $26.63   7.457%   $28.6158   $28.62   $28.60   $28.60  
  Purchase #4 $133.37   6.809%   $142.4512   $142.45   $142.45   $142.50  
  Purchase #5 $198.27   4.822%   $207.8306   $207.83   $207.85   $207.80  
  Purchase #6 $95.67   13.304%   $108.3979   $108.40   $108.40   $108.40  
  Purchase #7 $212.81   8.604%   $231.1202   $231.12   $231.10   $231.10  
  7 purchase totals = $872.17       $937.7771   $937.78   $937.75   $937.80