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 $14.54   10.135%   $16.0136   $16.01   $16.00   $16.00  
  Purchase #2 $183.75   12.176%   $206.1234   $206.12   $206.10   $206.10  
  Purchase #3 $156.67   5.435%   $165.185   $165.19   $165.20   $165.20  
  Purchase #4 $90.91   12.249%   $102.0456   $102.05   $102.05   $102.00  
  Purchase #5 $67.87   12.434%   $76.309   $76.31   $76.30   $76.30  
  Purchase #6 $25.54   6.558%   $27.2149   $27.21   $27.20   $27.20  
  Purchase #7 $227.28   13.431%   $257.806   $257.81   $257.80   $257.80  
  7 purchase totals = $766.56       $850.6975   $850.70   $850.65   $850.60