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 $186.61   6.586%   $198.9001   $198.90   $198.90   $198.90  
  Purchase #2 $171.55   4.729%   $179.6626   $179.66   $179.65   $179.70  
  Purchase #3 $56.64   8.737%   $61.5886   $61.59   $61.60   $61.60  
  Purchase #4 $19.34   3.776%   $20.0703   $20.07   $20.05   $20.10  
  Purchase #5 $134.84   5.825%   $142.6944   $142.69   $142.70   $142.70  
  Purchase #6 $116.26   6.432%   $123.7378   $123.74   $123.75   $123.70  
  Purchase #7 $98.83   7.420%   $106.1632   $106.16   $106.15   $106.20  
  7 purchase totals = $784.07       $832.8170   $832.81   $832.80   $832.90