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 $233.30   11.342%   $259.7609   $259.76   $259.75   $259.80  
  Purchase #2 $84.32   13.554%   $95.7487   $95.75   $95.75   $95.70  
  Purchase #3 $60.37   12.322%   $67.8088   $67.81   $67.80   $67.80  
  Purchase #4 $164.70   4.491%   $172.0967   $172.10   $172.10   $172.10  
  Purchase #5 $188.74   4.857%   $197.9071   $197.91   $197.90   $197.90  
  Purchase #6 $200.68   4.805%   $210.3227   $210.32   $210.30   $210.30  
  Purchase #7 $69.88   5.372%   $73.634   $73.63   $73.65   $73.60  
  7 purchase totals = $1,001.99       $1,077.2789   $1,077.28   $1,077.25   $1,077.20