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 $118.87   12.474%   $133.6978   $133.70   $133.70   $133.70  
  Purchase #2 $120.87   8.116%   $130.6798   $130.68   $130.70   $130.70  
  Purchase #3 $164.53   7.540%   $176.9356   $176.94   $176.95   $176.90  
  Purchase #4 $192.56   12.585%   $216.7937   $216.79   $216.80   $216.80  
  Purchase #5 $208.94   12.326%   $234.6939   $234.69   $234.70   $234.70  
  Purchase #6 $241.80   10.786%   $267.8805   $267.88   $267.90   $267.90  
  Purchase #7 $178.61   12.293%   $200.5665   $200.57   $200.55   $200.60  
  7 purchase totals = $1,226.18       $1,361.2478   $1,361.25   $1,361.30   $1,361.30