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 $63.83   6.862%   $68.21   $68.21   $68.20   $68.20  
  Purchase #2 $216.50   9.391%   $236.8315   $236.83   $236.85   $236.80  
  Purchase #3 $34.88   10.399%   $38.5072   $38.51   $38.50   $38.50  
  Purchase #4 $240.78   10.851%   $266.907   $266.91   $266.90   $266.90  
  Purchase #5 $106.57   10.826%   $118.1073   $118.11   $118.10   $118.10  
  Purchase #6 $27.97   9.664%   $30.673   $30.67   $30.65   $30.70  
  Purchase #7 $172.67   13.855%   $196.5934   $196.59   $196.60   $196.60  
  7 purchase totals = $863.20       $955.8294   $955.83   $955.80   $955.80