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 $177.39   8.660%   $192.752   $192.75   $192.75   $192.80  
  Purchase #2 $44.41   7.848%   $47.8953   $47.90   $47.90   $47.90  
  Purchase #3 $31.60   5.620%   $33.3759   $33.38   $33.40   $33.40  
  Purchase #4 $169.95   3.446%   $175.8065   $175.81   $175.80   $175.80  
  Purchase #5 $121.29   13.438%   $137.589   $137.59   $137.60   $137.60  
  Purchase #6 $145.85   12.379%   $163.9048   $163.90   $163.90   $163.90  
  Purchase #7 $247.81   3.260%   $255.8886   $255.89   $255.90   $255.90  
  7 purchase totals = $938.30       $1,007.2121   $1,007.22   $1,007.25   $1,007.30