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 $89.69   10.209%   $98.8465   $98.85   $98.85   $98.80  
  Purchase #2 $232.31   13.582%   $263.8623   $263.86   $263.85   $263.90  
  Purchase #3 $202.57   11.645%   $226.1593   $226.16   $226.15   $226.20  
  Purchase #4 $49.90   11.870%   $55.8231   $55.82   $55.80   $55.80  
  Purchase #5 $250.58   4.577%   $262.049   $262.05   $262.05   $262.00  
  Purchase #6 $245.79   8.274%   $266.1267   $266.13   $266.15   $266.10  
  Purchase #7 $249.61   5.656%   $263.7279   $263.73   $263.75   $263.70  
  7 purchase totals = $1,320.45       $1,436.5948   $1,436.60   $1,436.60   $1,436.50