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 $244.71   8.791%   $266.2225   $266.22   $266.20   $266.20  
  Purchase #2 $92.40   12.767%   $104.1967   $104.20   $104.20   $104.20  
  Purchase #3 $176.63   12.257%   $198.2795   $198.28   $198.30   $198.30  
  Purchase #4 $51.66   9.137%   $56.3802   $56.38   $56.40   $56.40  
  Purchase #5 $46.43   8.558%   $50.4035   $50.40   $50.40   $50.40  
  Purchase #6 $196.53   8.608%   $213.4473   $213.45   $213.45   $213.40  
  Purchase #7 $113.38   3.666%   $117.5365   $117.54   $117.55   $117.50  
  7 purchase totals = $921.74       $1,006.4662   $1,006.47   $1,006.50   $1,006.40