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 $239.67   10.714%   $265.3482   $265.35   $265.35   $265.30  
  Purchase #2 $246.95   4.422%   $257.8701   $257.87   $257.85   $257.90  
  Purchase #3 $154.86   10.823%   $171.6205   $171.62   $171.60   $171.60  
  Purchase #4 $103.99   11.199%   $115.6358   $115.64   $115.65   $115.60  
  Purchase #5 $76.25   6.409%   $81.1369   $81.14   $81.15   $81.10  
  Purchase #6 $9.33   13.787%   $10.6163   $10.62   $10.60   $10.60  
  Purchase #7 $119.59   8.294%   $129.5088   $129.51   $129.50   $129.50  
  7 purchase totals = $950.64       $1,031.7366   $1,031.75   $1,031.70   $1,031.60