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 $202.84   11.462%   $226.0895   $226.09   $226.10   $226.10  
  Purchase #2 $157.44   4.199%   $164.0509   $164.05   $164.05   $164.10  
  Purchase #3 $110.73   5.730%   $117.0748   $117.07   $117.05   $117.10  
  Purchase #4 $207.74   4.235%   $216.5378   $216.54   $216.55   $216.50  
  Purchase #5 $108.26   7.816%   $116.7216   $116.72   $116.70   $116.70  
  Purchase #6 $57.81   6.256%   $61.4266   $61.43   $61.45   $61.40  
  Purchase #7 $144.99   11.370%   $161.4754   $161.48   $161.50   $161.50  
  7 purchase totals = $989.81       $1,063.3766   $1,063.38   $1,063.40   $1,063.40