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 $172.27   12.177%   $193.2473   $193.25   $193.25   $193.20  
  Purchase #2 $130.54   4.337%   $136.2015   $136.20   $136.20   $136.20  
  Purchase #3 $179.61   11.703%   $200.6298   $200.63   $200.65   $200.60  
  Purchase #4 $188.27   9.279%   $205.7396   $205.74   $205.75   $205.70  
  Purchase #5 $127.37   11.234%   $141.6787   $141.68   $141.70   $141.70  
  Purchase #6 $233.48   13.441%   $264.862   $264.86   $264.85   $264.90  
  Purchase #7 $150.86   9.532%   $165.24   $165.24   $165.25   $165.20  
  7 purchase totals = $1,182.40       $1,307.5989   $1,307.60   $1,307.65   $1,307.50