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 $119.69   13.305%   $135.6148   $135.61   $135.60   $135.60  
  Purchase #2 $136.30   12.661%   $153.5569   $153.56   $153.55   $153.60  
  Purchase #3 $26.97   9.250%   $29.4647   $29.46   $29.45   $29.50  
  Purchase #4 $241.32   12.210%   $270.7852   $270.79   $270.80   $270.80  
  Purchase #5 $136.69   4.522%   $142.8711   $142.87   $142.85   $142.90  
  Purchase #6 $79.27   11.863%   $88.6738   $88.67   $88.65   $88.70  
  Purchase #7 $140.95   8.838%   $153.4072   $153.41   $153.40   $153.40  
  7 purchase totals = $881.19       $974.3737   $974.37   $974.30   $974.50