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 $57.55   7.267%   $61.7322   $61.73   $61.75   $61.70  
  Purchase #2 $51.90   8.189%   $56.1501   $56.15   $56.15   $56.20  
  Purchase #3 $238.51   11.193%   $265.2064   $265.21   $265.20   $265.20  
  Purchase #4 $183.50   8.385%   $198.8865   $198.89   $198.90   $198.90  
  Purchase #5 $60.45   7.558%   $65.0188   $65.02   $65.00   $65.00  
  Purchase #6 $69.51   7.762%   $74.9054   $74.91   $74.90   $74.90  
  Purchase #7 $35.58   6.654%   $37.9475   $37.95   $37.95   $37.90  
  7 purchase totals = $697.00       $759.8469   $759.86   $759.85   $759.80