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 $236.27   12.264%   $265.2462   $265.25   $265.25   $265.20  
  Purchase #2 $242.53   13.145%   $274.4106   $274.41   $274.40   $274.40  
  Purchase #3 $25.57   3.447%   $26.4514   $26.45   $26.45   $26.50  
  Purchase #4 $151.69   7.753%   $163.4505   $163.45   $163.45   $163.50  
  Purchase #5 $248.75   12.700%   $280.3413   $280.34   $280.35   $280.30  
  Purchase #6 $32.28   10.564%   $35.6901   $35.69   $35.70   $35.70  
  Purchase #7 $81.97   7.380%   $88.0194   $88.02   $88.00   $88.00  
  7 purchase totals = $1,019.06       $1,133.6095   $1,133.61   $1,133.60   $1,133.60