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 $52.62   11.302%   $58.5671   $58.57   $58.55   $58.60  
  Purchase #2 $178.86   6.732%   $190.9009   $190.90   $190.90   $190.90  
  Purchase #3 $248.67   3.465%   $257.2864   $257.29   $257.30   $257.30  
  Purchase #4 $210.27   5.773%   $222.4089   $222.41   $222.40   $222.40  
  Purchase #5 $44.91   11.706%   $50.1672   $50.17   $50.15   $50.20  
  Purchase #6 $199.49   9.133%   $217.7094   $217.71   $217.70   $217.70  
  Purchase #7 $136.29   3.376%   $140.8912   $140.89   $140.90   $140.90  
  7 purchase totals = $1,071.11       $1,137.9311   $1,137.94   $1,137.90   $1,138.00