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 $236.71   13.274%   $268.1309   $268.13   $268.15   $268.10  
  Purchase #2 $54.35   13.312%   $61.5851   $61.59   $61.60   $61.60  
  Purchase #3 $10.37   12.126%   $11.6275   $11.63   $11.65   $11.60  
  Purchase #4 $13.79   5.738%   $14.5813   $14.58   $14.60   $14.60  
  Purchase #5 $216.27   6.344%   $229.9902   $229.99   $230.00   $230.00  
  Purchase #6 $75.94   12.416%   $85.3687   $85.37   $85.35   $85.40  
  Purchase #7 $68.91   13.425%   $78.1612   $78.16   $78.15   $78.20  
  7 purchase totals = $676.34       $749.4449   $749.45   $749.50   $749.50