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 $247.83   5.615%   $261.7457   $261.75   $261.75   $261.70  
  Purchase #2 $219.96   4.686%   $230.2673   $230.27   $230.25   $230.30  
  Purchase #3 $88.51   9.700%   $97.0955   $97.10   $97.10   $97.10  
  Purchase #4 $166.94   6.349%   $177.539   $177.54   $177.55   $177.50  
  Purchase #5 $51.71   9.761%   $56.7574   $56.76   $56.75   $56.80  
  Purchase #6 $81.55   4.700%   $85.3829   $85.38   $85.40   $85.40  
  Purchase #7 $119.89   10.175%   $132.0888   $132.09   $132.10   $132.10  
  7 purchase totals = $976.39       $1,040.8766   $1,040.89   $1,040.90   $1,040.90