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 $94.92   4.204%   $98.9104   $98.91   $98.90   $98.90  
  Purchase #2 $178.37   6.774%   $190.4528   $190.45   $190.45   $190.50  
  Purchase #3 $250.55   5.433%   $264.1624   $264.16   $264.15   $264.20  
  Purchase #4 $152.74   8.605%   $165.8833   $165.88   $165.90   $165.90  
  Purchase #5 $20.97   11.259%   $23.331   $23.33   $23.35   $23.30  
  Purchase #6 $145.26   7.131%   $155.6185   $155.62   $155.60   $155.60  
  Purchase #7 $111.99   12.735%   $126.2519   $126.25   $126.25   $126.30  
  7 purchase totals = $954.80       $1,024.6103   $1,024.60   $1,024.60   $1,024.70