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 $247.49   5.161%   $260.263   $260.26   $260.25   $260.30  
  Purchase #2 $60.44   5.403%   $63.7056   $63.71   $63.70   $63.70  
  Purchase #3 $16.62   5.565%   $17.5449   $17.54   $17.55   $17.50  
  Purchase #4 $159.61   9.372%   $174.5686   $174.57   $174.55   $174.60  
  Purchase #5 $140.83   8.124%   $152.271   $152.27   $152.25   $152.30  
  Purchase #6 $224.92   10.219%   $247.9046   $247.90   $247.90   $247.90  
  Purchase #7 $140.32   9.612%   $153.8076   $153.81   $153.80   $153.80  
  7 purchase totals = $990.23       $1,070.0653   $1,070.06   $1,070.00   $1,070.10