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 $238.25   10.338%   $262.8803   $262.88   $262.90   $262.90  
  Purchase #2 $149.95   13.487%   $170.1738   $170.17   $170.15   $170.20  
  Purchase #3 $236.67   12.442%   $266.1165   $266.12   $266.10   $266.10  
  Purchase #4 $172.53   6.418%   $183.603   $183.60   $183.60   $183.60  
  Purchase #5 $227.88   8.384%   $246.9855   $246.99   $247.00   $247.00  
  Purchase #6 $151.70   7.468%   $163.029   $163.03   $163.05   $163.00  
  Purchase #7 $207.28   13.174%   $234.5871   $234.59   $234.60   $234.60  
  7 purchase totals = $1,384.26       $1,527.3752   $1,527.38   $1,527.40   $1,527.40