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 $86.72   12.531%   $97.5869   $97.59   $97.60   $97.60  
  Purchase #2 $149.68   11.492%   $166.8812   $166.88   $166.90   $166.90  
  Purchase #3 $71.79   8.224%   $77.694   $77.69   $77.70   $77.70  
  Purchase #4 $24.29   5.663%   $25.6655   $25.67   $25.65   $25.70  
  Purchase #5 $42.37   12.597%   $47.7073   $47.71   $47.70   $47.70  
  Purchase #6 $96.78   9.401%   $105.8783   $105.88   $105.90   $105.90  
  Purchase #7 $244.63   10.257%   $269.7217   $269.72   $269.70   $269.70  
  7 purchase totals = $716.26       $791.1349   $791.14   $791.15   $791.20