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 $85.58   3.509%   $88.583   $88.58   $88.60   $88.60  
  Purchase #2 $196.60   9.160%   $214.6086   $214.61   $214.60   $214.60  
  Purchase #3 $108.92   5.580%   $114.9977   $115.00   $115.00   $115.00  
  Purchase #4 $52.25   12.825%   $58.9511   $58.95   $58.95   $59.00  
  Purchase #5 $62.46   6.768%   $66.6873   $66.69   $66.70   $66.70  
  Purchase #6 $224.61   4.373%   $234.4322   $234.43   $234.45   $234.40  
  Purchase #7 $53.81   5.654%   $56.8524   $56.85   $56.85   $56.90  
  7 purchase totals = $784.23       $835.1123   $835.11   $835.15   $835.20