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 $206.30   13.787%   $234.7426   $234.74   $234.75   $234.70  
  Purchase #2 $176.51   12.678%   $198.8879   $198.89   $198.90   $198.90  
  Purchase #3 $93.74   5.255%   $98.666   $98.67   $98.65   $98.70  
  Purchase #4 $142.41   11.344%   $158.565   $158.57   $158.55   $158.60  
  Purchase #5 $241.77   10.804%   $267.8908   $267.89   $267.90   $267.90  
  Purchase #6 $158.29   11.773%   $176.9255   $176.93   $176.95   $176.90  
  Purchase #7 $85.63   6.177%   $90.9194   $90.92   $90.90   $90.90  
  7 purchase totals = $1,104.65       $1,226.5972   $1,226.61   $1,226.60   $1,226.60