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 $215.65   11.155%   $239.7058   $239.71   $239.70   $239.70  
  Purchase #2 $81.33   12.604%   $91.5808   $91.58   $91.60   $91.60  
  Purchase #3 $152.73   7.774%   $164.6032   $164.60   $164.60   $164.60  
  Purchase #4 $75.66   9.555%   $82.8893   $82.89   $82.90   $82.90  
  Purchase #5 $81.56   6.106%   $86.5401   $86.54   $86.55   $86.50  
  Purchase #6 $161.48   5.145%   $169.7881   $169.79   $169.80   $169.80  
  Purchase #7 $148.63   7.109%   $159.1961   $159.20   $159.20   $159.20  
  7 purchase totals = $917.04       $994.3034   $994.31   $994.35   $994.30