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 $111.55   13.619%   $126.742   $126.74   $126.75   $126.70  
  Purchase #2 $20.74   13.192%   $23.476   $23.48   $23.50   $23.50  
  Purchase #3 $25.92   4.848%   $27.1766   $27.18   $27.20   $27.20  
  Purchase #4 $228.83   3.453%   $236.7315   $236.73   $236.75   $236.70  
  Purchase #5 $49.82   13.705%   $56.6478   $56.65   $56.65   $56.60  
  Purchase #6 $236.51   12.663%   $266.4593   $266.46   $266.45   $266.50  
  Purchase #7 $32.32   13.508%   $36.6858   $36.69   $36.70   $36.70  
  7 purchase totals = $705.69       $773.9190   $773.93   $774.00   $773.90