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 $157.66   13.726%   $179.3004   $179.30   $179.30   $179.30  
  Purchase #2 $249.63   8.526%   $270.9135   $270.91   $270.90   $270.90  
  Purchase #3 $152.91   8.726%   $166.2529   $166.25   $166.25   $166.30  
  Purchase #4 $243.92   11.556%   $272.1074   $272.11   $272.10   $272.10  
  Purchase #5 $227.58   8.158%   $246.146   $246.15   $246.15   $246.10  
  Purchase #6 $231.57   8.798%   $251.9435   $251.94   $251.95   $251.90  
  Purchase #7 $164.64   7.291%   $176.6439   $176.64   $176.65   $176.60  
  7 purchase totals = $1,427.91       $1,563.3076   $1,563.30   $1,563.30   $1,563.20