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 $161.68   3.342%   $167.0833   $167.08   $167.10   $167.10  
  Purchase #2 $22.87   13.683%   $25.9993   $26.00   $26.00   $26.00  
  Purchase #3 $70.91   10.566%   $78.4024   $78.40   $78.40   $78.40  
  Purchase #4 $221.43   3.400%   $228.9586   $228.96   $228.95   $229.00  
  Purchase #5 $247.55   5.613%   $261.445   $261.45   $261.45   $261.40  
  Purchase #6 $12.47   11.387%   $13.89   $13.89   $13.90   $13.90  
  Purchase #7 $125.38   12.658%   $141.2506   $141.25   $141.25   $141.30  
  7 purchase totals = $862.29       $917.0292   $917.03   $917.05   $917.10