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 $225.83   6.567%   $240.6603   $240.66   $240.65   $240.70  
  Purchase #2 $184.42   6.650%   $196.6839   $196.68   $196.70   $196.70  
  Purchase #3 $70.50   4.172%   $73.4413   $73.44   $73.45   $73.40  
  Purchase #4 $205.94   6.791%   $219.9254   $219.93   $219.95   $219.90  
  Purchase #5 $182.64   6.473%   $194.4623   $194.46   $194.45   $194.50  
  Purchase #6 $44.41   13.200%   $50.2721   $50.27   $50.25   $50.30  
  Purchase #7 $51.68   13.128%   $58.4646   $58.46   $58.45   $58.50  
  7 purchase totals = $965.42       $1,033.9099   $1,033.90   $1,033.90   $1,034.00