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 $34.61   10.500%   $38.2441   $38.24   $38.25   $38.20  
  Purchase #2 $98.97   4.193%   $103.1198   $103.12   $103.10   $103.10  
  Purchase #3 $48.80   11.791%   $54.554   $54.55   $54.55   $54.60  
  Purchase #4 $163.53   11.572%   $182.4537   $182.45   $182.45   $182.50  
  Purchase #5 $23.97   3.580%   $24.8281   $24.83   $24.85   $24.80  
  Purchase #6 $228.73   8.208%   $247.5042   $247.50   $247.50   $247.50  
  Purchase #7 $108.51   4.563%   $113.4613   $113.46   $113.45   $113.50  
  7 purchase totals = $707.12       $764.1652   $764.15   $764.15   $764.20