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 $116.73   13.872%   $132.9228   $132.92   $132.90   $132.90  
  Purchase #2 $239.44   8.352%   $259.438   $259.44   $259.45   $259.40  
  Purchase #3 $167.83   8.732%   $182.4849   $182.48   $182.50   $182.50  
  Purchase #4 $17.58   12.386%   $19.7575   $19.76   $19.75   $19.80  
  Purchase #5 $163.94   6.488%   $174.5764   $174.58   $174.60   $174.60  
  Purchase #6 $102.55   11.268%   $114.1053   $114.11   $114.10   $114.10  
  Purchase #7 $172.58   10.433%   $190.5853   $190.59   $190.60   $190.60  
  7 purchase totals = $980.65       $1,073.8702   $1,073.88   $1,073.90   $1,073.90