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 $208.94   12.329%   $234.7002   $234.70   $234.70   $234.70  
  Purchase #2 $212.42   8.220%   $229.8809   $229.88   $229.90   $229.90  
  Purchase #3 $71.56   3.175%   $73.832   $73.83   $73.85   $73.80  
  Purchase #4 $247.96   4.867%   $260.0282   $260.03   $260.05   $260.00  
  Purchase #5 $153.62   10.168%   $169.2401   $169.24   $169.25   $169.20  
  Purchase #6 $78.48   5.874%   $83.0899   $83.09   $83.10   $83.10  
  Purchase #7 $193.26   11.688%   $215.8482   $215.85   $215.85   $215.80  
  7 purchase totals = $1,166.24       $1,266.6195   $1,266.62   $1,266.70   $1,266.50