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 $23.69   11.783%   $26.4814   $26.48   $26.50   $26.50  
  Purchase #2 $121.69   9.693%   $133.4854   $133.49   $133.50   $133.50  
  Purchase #3 $192.50   11.483%   $214.6048   $214.60   $214.60   $214.60  
  Purchase #4 $212.93   11.596%   $237.6214   $237.62   $237.60   $237.60  
  Purchase #5 $198.87   12.731%   $224.1881   $224.19   $224.20   $224.20  
  Purchase #6 $69.99   3.410%   $72.3767   $72.38   $72.40   $72.40  
  Purchase #7 $102.93   10.349%   $113.5822   $113.58   $113.60   $113.60  
  7 purchase totals = $922.60       $1,022.3400   $1,022.34   $1,022.40   $1,022.40