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 $237.79   12.576%   $267.6945   $267.69   $267.70   $267.70  
  Purchase #2 $236.62   4.283%   $246.7544   $246.75   $246.75   $246.80  
  Purchase #3 $67.71   10.128%   $74.5677   $74.57   $74.55   $74.60  
  Purchase #4 $200.89   11.535%   $224.0627   $224.06   $224.05   $224.10  
  Purchase #5 $173.37   8.575%   $188.2365   $188.24   $188.25   $188.20  
  Purchase #6 $158.53   12.809%   $178.8361   $178.84   $178.85   $178.80  
  Purchase #7 $138.87   5.529%   $146.5481   $146.55   $146.55   $146.50  
  7 purchase totals = $1,213.78       $1,326.7000   $1,326.70   $1,326.70   $1,326.70