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 $104.70   9.323%   $114.4612   $114.46   $114.45   $114.50  
  Purchase #2 $247.95   10.322%   $273.5434   $273.54   $273.55   $273.50  
  Purchase #3 $84.51   8.447%   $91.6486   $91.65   $91.65   $91.60  
  Purchase #4 $82.74   7.422%   $88.881   $88.88   $88.90   $88.90  
  Purchase #5 $127.94   9.726%   $140.3834   $140.38   $140.40   $140.40  
  Purchase #6 $157.69   3.668%   $163.4741   $163.47   $163.45   $163.50  
  Purchase #7 $173.43   11.285%   $193.0016   $193.00   $193.00   $193.00  
  7 purchase totals = $978.96       $1,065.3933   $1,065.38   $1,065.40   $1,065.40