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 $30.87   4.786%   $32.3474   $32.35   $32.35   $32.30  
  Purchase #2 $164.34   12.515%   $184.9072   $184.91   $184.90   $184.90  
  Purchase #3 $244.91   11.626%   $273.3832   $273.38   $273.40   $273.40  
  Purchase #4 $210.61   12.677%   $237.309   $237.31   $237.30   $237.30  
  Purchase #5 $153.67   7.611%   $165.3658   $165.37   $165.35   $165.40  
  Purchase #6 $210.28   10.734%   $232.8515   $232.85   $232.85   $232.90  
  Purchase #7 $13.34   13.674%   $15.1641   $15.16   $15.15   $15.20  
  7 purchase totals = $1,028.02       $1,141.3282   $1,141.33   $1,141.30   $1,141.40