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 $182.76   6.302%   $194.2775   $194.28   $194.30   $194.30  
  Purchase #2 $70.94   10.387%   $78.3085   $78.31   $78.30   $78.30  
  Purchase #3 $158.50   9.336%   $173.2976   $173.30   $173.30   $173.30  
  Purchase #4 $231.76   7.708%   $249.6241   $249.62   $249.60   $249.60  
  Purchase #5 $45.44   10.158%   $50.0558   $50.06   $50.05   $50.10  
  Purchase #6 $154.70   12.262%   $173.6693   $173.67   $173.65   $173.70  
  Purchase #7 $67.98   12.132%   $76.2273   $76.23   $76.25   $76.20  
  7 purchase totals = $912.08       $995.4601   $995.47   $995.45   $995.50