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 $246.26   3.859%   $255.7632   $255.76   $255.75   $255.80  
  Purchase #2 $105.51   8.702%   $114.6915   $114.69   $114.70   $114.70  
  Purchase #3 $6.76   13.309%   $7.6597   $7.66   $7.65   $7.70  
  Purchase #4 $188.28   7.158%   $201.7571   $201.76   $201.75   $201.80  
  Purchase #5 $219.78   3.227%   $226.8723   $226.87   $226.85   $226.90  
  Purchase #6 $13.61   4.754%   $14.257   $14.26   $14.25   $14.30  
  Purchase #7 $178.38   9.148%   $194.6982   $194.70   $194.70   $194.70  
  7 purchase totals = $958.58       $1,015.6990   $1,015.70   $1,015.65   $1,015.90