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 $65.77   11.147%   $73.1014   $73.10   $73.10   $73.10  
  Purchase #2 $162.28   13.361%   $183.9622   $183.96   $183.95   $184.00  
  Purchase #3 $72.28   7.777%   $77.9012   $77.90   $77.90   $77.90  
  Purchase #4 $113.43   12.603%   $127.7256   $127.73   $127.75   $127.70  
  Purchase #5 $95.46   3.435%   $98.7391   $98.74   $98.75   $98.70  
  Purchase #6 $145.53   13.762%   $165.5578   $165.56   $165.55   $165.60  
  Purchase #7 $123.77   12.159%   $138.8192   $138.82   $138.80   $138.80  
  7 purchase totals = $778.52       $865.8065   $865.81   $865.80   $865.80