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 $214.63   6.392%   $228.3491   $228.35   $228.35   $228.30  
  Purchase #2 $164.35   6.273%   $174.6597   $174.66   $174.65   $174.70  
  Purchase #3 $236.48   8.465%   $256.498   $256.50   $256.50   $256.50  
  Purchase #4 $55.64   13.391%   $63.0908   $63.09   $63.10   $63.10  
  Purchase #5 $85.59   11.323%   $95.2814   $95.28   $95.30   $95.30  
  Purchase #6 $62.27   10.394%   $68.7423   $68.74   $68.75   $68.70  
  Purchase #7 $158.36   4.680%   $165.7712   $165.77   $165.75   $165.80  
  7 purchase totals = $977.32       $1,052.3925   $1,052.39   $1,052.40   $1,052.40