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 $56.98   7.765%   $61.4045   $61.40   $61.40   $61.40  
  Purchase #2 $190.61   11.844%   $213.1858   $213.19   $213.20   $213.20  
  Purchase #3 $130.61   11.411%   $145.5139   $145.51   $145.50   $145.50  
  Purchase #4 $6.78   5.855%   $7.177   $7.18   $7.20   $7.20  
  Purchase #5 $141.67   11.452%   $157.894   $157.89   $157.90   $157.90  
  Purchase #6 $214.35   11.293%   $238.5565   $238.56   $238.55   $238.60  
  Purchase #7 $85.27   4.281%   $88.9204   $88.92   $88.90   $88.90  
  7 purchase totals = $826.27       $912.6521   $912.65   $912.65   $912.70