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 $107.42   8.274%   $116.3079   $116.31   $116.30   $116.30  
  Purchase #2 $237.90   8.171%   $257.3388   $257.34   $257.35   $257.30  
  Purchase #3 $125.62   11.445%   $139.9972   $140.00   $140.00   $140.00  
  Purchase #4 $182.37   8.872%   $198.5499   $198.55   $198.55   $198.50  
  Purchase #5 $241.68   4.713%   $253.0704   $253.07   $253.05   $253.10  
  Purchase #6 $212.73   10.605%   $235.29   $235.29   $235.30   $235.30  
  Purchase #7 $151.44   11.262%   $168.4952   $168.50   $168.50   $168.50  
  7 purchase totals = $1,259.16       $1,369.0494   $1,369.06   $1,369.05   $1,369.00