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 $176.97   5.303%   $186.3547   $186.35   $186.35   $186.40  
  Purchase #2 $236.93   10.148%   $260.9737   $260.97   $260.95   $261.00  
  Purchase #3 $245.51   7.524%   $263.9822   $263.98   $264.00   $264.00  
  Purchase #4 $81.31   9.791%   $89.2711   $89.27   $89.25   $89.30  
  Purchase #5 $59.92   6.619%   $63.8861   $63.89   $63.90   $63.90  
  Purchase #6 $15.76   6.306%   $16.7538   $16.75   $16.75   $16.80  
  Purchase #7 $60.46   4.695%   $63.2986   $63.30   $63.30   $63.30  
  7 purchase totals = $876.86       $944.5202   $944.51   $944.50   $944.70