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 $85.62   8.515%   $92.9105   $92.91   $92.90   $92.90  
  Purchase #2 $249.80   9.714%   $274.0656   $274.07   $274.05   $274.10  
  Purchase #3 $118.81   12.402%   $133.5448   $133.54   $133.55   $133.50  
  Purchase #4 $155.37   5.526%   $163.9557   $163.96   $163.95   $164.00  
  Purchase #5 $222.99   8.316%   $241.5338   $241.53   $241.55   $241.50  
  Purchase #6 $97.31   8.493%   $105.5745   $105.57   $105.55   $105.60  
  Purchase #7 $186.35   8.789%   $202.7283   $202.73   $202.75   $202.70  
  7 purchase totals = $1,116.25       $1,214.3132   $1,214.31   $1,214.30   $1,214.30