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 $58.63   8.788%   $63.7824   $63.78   $63.80   $63.80  
  Purchase #2 $157.71   11.756%   $176.2504   $176.25   $176.25   $176.30  
  Purchase #3 $150.86   9.746%   $165.5628   $165.56   $165.55   $165.60  
  Purchase #4 $195.33   9.655%   $214.1891   $214.19   $214.20   $214.20  
  Purchase #5 $198.70   8.478%   $215.5458   $215.55   $215.55   $215.50  
  Purchase #6 $46.99   6.747%   $50.1604   $50.16   $50.15   $50.20  
  Purchase #7 $212.59   8.732%   $231.1534   $231.15   $231.15   $231.20  
  7 purchase totals = $1,020.81       $1,116.6443   $1,116.64   $1,116.65   $1,116.80