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 $244.36   9.461%   $267.4789   $267.48   $267.50   $267.50  
  Purchase #2 $100.70   6.274%   $107.0179   $107.02   $107.00   $107.00  
  Purchase #3 $44.44   7.587%   $47.8117   $47.81   $47.80   $47.80  
  Purchase #4 $164.29   5.169%   $172.7822   $172.78   $172.80   $172.80  
  Purchase #5 $41.65   10.334%   $45.9541   $45.95   $45.95   $46.00  
  Purchase #6 $156.87   12.673%   $176.7501   $176.75   $176.75   $176.80  
  Purchase #7 $235.29   9.859%   $258.4872   $258.49   $258.50   $258.50  
  7 purchase totals = $987.60       $1,076.2821   $1,076.28   $1,076.30   $1,076.40