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 $67.73   8.111%   $73.2236   $73.22   $73.20   $73.20  
  Purchase #2 $209.49   4.390%   $218.6866   $218.69   $218.70   $218.70  
  Purchase #3 $111.82   8.452%   $121.271   $121.27   $121.25   $121.30  
  Purchase #4 $176.89   9.494%   $193.6839   $193.68   $193.70   $193.70  
  Purchase #5 $138.87   8.104%   $150.124   $150.12   $150.10   $150.10  
  Purchase #6 $11.40   9.393%   $12.4708   $12.47   $12.45   $12.50  
  Purchase #7 $135.27   4.177%   $140.9202   $140.92   $140.90   $140.90  
  7 purchase totals = $851.47       $910.3801   $910.37   $910.30   $910.40