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 $136.64   11.206%   $151.9519   $151.95   $151.95   $152.00  
  Purchase #2 $121.31   10.440%   $133.9748   $133.97   $133.95   $134.00  
  Purchase #3 $179.84   12.216%   $201.8093   $201.81   $201.80   $201.80  
  Purchase #4 $134.54   6.161%   $142.829   $142.83   $142.85   $142.80  
  Purchase #5 $197.55   9.550%   $216.416   $216.42   $216.40   $216.40  
  Purchase #6 $248.96   12.102%   $279.0891   $279.09   $279.10   $279.10  
  Purchase #7 $197.97   12.604%   $222.9221   $222.92   $222.90   $222.90  
  7 purchase totals = $1,216.81       $1,348.9922   $1,348.99   $1,348.95   $1,349.00