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 $195.55   6.357%   $207.9811   $207.98   $208.00   $208.00  
  Purchase #2 $47.45   8.225%   $51.3528   $51.35   $51.35   $51.40  
  Purchase #3 $46.70   3.804%   $48.4765   $48.48   $48.50   $48.50  
  Purchase #4 $209.42   11.626%   $233.7672   $233.77   $233.75   $233.80  
  Purchase #5 $234.88   12.536%   $264.3246   $264.32   $264.30   $264.30  
  Purchase #6 $250.32   3.717%   $259.6244   $259.62   $259.60   $259.60  
  Purchase #7 $241.76   11.597%   $269.7969   $269.80   $269.80   $269.80  
  7 purchase totals = $1,226.08       $1,335.3235   $1,335.32   $1,335.30   $1,335.40