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 $151.74   6.133%   $161.0462   $161.05   $161.05   $161.00  
  Purchase #2 $203.61   9.353%   $222.6536   $222.65   $222.65   $222.70  
  Purchase #3 $11.49   7.704%   $12.3752   $12.38   $12.40   $12.40  
  Purchase #4 $131.28   8.329%   $142.2143   $142.21   $142.20   $142.20  
  Purchase #5 $124.48   9.688%   $136.5396   $136.54   $136.55   $136.50  
  Purchase #6 $19.85   10.810%   $21.9958   $22.00   $22.00   $22.00  
  Purchase #7 $15.70   11.396%   $17.4892   $17.49   $17.50   $17.50  
  7 purchase totals = $658.15       $714.3139   $714.32   $714.35   $714.30