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 $83.66   11.289%   $93.1044   $93.10   $93.10   $93.10  
  Purchase #2 $248.29   3.416%   $256.7716   $256.77   $256.75   $256.80  
  Purchase #3 $69.98   10.847%   $77.5707   $77.57   $77.55   $77.60  
  Purchase #4 $217.25   10.498%   $240.0569   $240.06   $240.05   $240.10  
  Purchase #5 $176.66   13.617%   $200.7158   $200.72   $200.70   $200.70  
  Purchase #6 $87.89   12.340%   $98.7356   $98.74   $98.75   $98.70  
  Purchase #7 $44.98   5.628%   $47.5115   $47.51   $47.50   $47.50  
  7 purchase totals = $928.71       $1,014.4665   $1,014.47   $1,014.40   $1,014.50