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 $186.59   5.496%   $196.845   $196.85   $196.85   $196.80  
  Purchase #2 $63.75   7.820%   $68.7353   $68.74   $68.75   $68.70  
  Purchase #3 $113.64   5.669%   $120.0823   $120.08   $120.10   $120.10  
  Purchase #4 $248.92   5.233%   $261.946   $261.95   $261.95   $261.90  
  Purchase #5 $89.31   10.769%   $98.9278   $98.93   $98.95   $98.90  
  Purchase #6 $35.85   5.463%   $37.8085   $37.81   $37.80   $37.80  
  Purchase #7 $12.77   6.479%   $13.5974   $13.60   $13.60   $13.60  
  7 purchase totals = $750.83       $797.9423   $797.96   $798.00   $797.80