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 $59.47   6.258%   $63.1916   $63.19   $63.20   $63.20  
  Purchase #2 $218.83   9.429%   $239.4635   $239.46   $239.45   $239.50  
  Purchase #3 $190.46   9.557%   $208.6623   $208.66   $208.65   $208.70  
  Purchase #4 $116.35   5.351%   $122.5759   $122.58   $122.60   $122.60  
  Purchase #5 $92.88   10.216%   $102.3686   $102.37   $102.35   $102.40  
  Purchase #6 $119.41   6.310%   $126.9448   $126.94   $126.95   $126.90  
  Purchase #7 $157.35   7.514%   $169.1733   $169.17   $169.15   $169.20  
  7 purchase totals = $954.75       $1,032.3800   $1,032.37   $1,032.35   $1,032.50