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 $119.45   12.292%   $134.1328   $134.13   $134.15   $134.10  
  Purchase #2 $24.28   5.337%   $25.5758   $25.58   $25.60   $25.60  
  Purchase #3 $131.31   3.432%   $135.8166   $135.82   $135.80   $135.80  
  Purchase #4 $56.94   6.379%   $60.5722   $60.57   $60.55   $60.60  
  Purchase #5 $104.50   9.125%   $114.0356   $114.04   $114.05   $114.00  
  Purchase #6 $220.54   9.496%   $241.4825   $241.48   $241.50   $241.50  
  Purchase #7 $244.90   10.627%   $270.9255   $270.93   $270.95   $270.90  
  7 purchase totals = $901.92       $982.5410   $982.55   $982.60   $982.50