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 $113.98   10.819%   $126.3115   $126.31   $126.30   $126.30  
  Purchase #2 $238.47   12.728%   $268.8225   $268.82   $268.80   $268.80  
  Purchase #3 $215.54   5.527%   $227.4529   $227.45   $227.45   $227.50  
  Purchase #4 $218.89   13.458%   $248.3482   $248.35   $248.35   $248.30  
  Purchase #5 $224.32   7.167%   $240.397   $240.40   $240.40   $240.40  
  Purchase #6 $181.75   11.749%   $203.1038   $203.10   $203.10   $203.10  
  Purchase #7 $73.26   4.549%   $76.5926   $76.59   $76.60   $76.60  
  7 purchase totals = $1,266.21       $1,391.0285   $1,391.02   $1,391.00   $1,391.00