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 $104.96   13.285%   $118.9039   $118.90   $118.90   $118.90  
  Purchase #2 $91.54   4.289%   $95.4662   $95.47   $95.45   $95.50  
  Purchase #3 $110.38   3.421%   $114.1561   $114.16   $114.15   $114.20  
  Purchase #4 $238.66   9.115%   $260.4139   $260.41   $260.40   $260.40  
  Purchase #5 $208.83   9.792%   $229.2786   $229.28   $229.30   $229.30  
  Purchase #6 $172.44   4.134%   $179.5687   $179.57   $179.55   $179.60  
  Purchase #7 $176.58   9.715%   $193.7347   $193.73   $193.75   $193.70  
  7 purchase totals = $1,103.39       $1,191.5221   $1,191.52   $1,191.50   $1,191.60