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 $197.40   8.522%   $214.2224   $214.22   $214.20   $214.20  
  Purchase #2 $202.64   11.841%   $226.6346   $226.63   $226.65   $226.60  
  Purchase #3 $81.38   5.349%   $85.733   $85.73   $85.75   $85.70  
  Purchase #4 $244.56   12.436%   $274.9735   $274.97   $274.95   $275.00  
  Purchase #5 $245.88   6.783%   $262.558   $262.56   $262.55   $262.60  
  Purchase #6 $178.34   6.629%   $190.1622   $190.16   $190.15   $190.20  
  Purchase #7 $114.32   10.219%   $126.0024   $126.00   $126.00   $126.00  
  7 purchase totals = $1,264.52       $1,380.2861   $1,380.27   $1,380.25   $1,380.30