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 $136.87   10.655%   $151.4535   $151.45   $151.45   $151.50  
  Purchase #2 $94.93   7.607%   $102.1513   $102.15   $102.15   $102.20  
  Purchase #3 $144.61   13.127%   $163.593   $163.59   $163.60   $163.60  
  Purchase #4 $165.75   12.623%   $186.6726   $186.67   $186.65   $186.70  
  Purchase #5 $197.67   13.398%   $224.1538   $224.15   $224.15   $224.20  
  Purchase #6 $66.60   7.271%   $71.4425   $71.44   $71.45   $71.40  
  Purchase #7 $116.59   4.823%   $122.2131   $122.21   $122.20   $122.20  
  7 purchase totals = $923.02       $1,021.6798   $1,021.66   $1,021.65   $1,021.80