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 $96.29   8.268%   $104.2513   $104.25   $104.25   $104.30  
  Purchase #2 $184.54   7.280%   $197.9745   $197.97   $197.95   $198.00  
  Purchase #3 $185.37   7.346%   $198.9873   $198.99   $199.00   $199.00  
  Purchase #4 $66.52   6.535%   $70.8671   $70.87   $70.85   $70.90  
  Purchase #5 $91.37   9.465%   $100.0182   $100.02   $100.00   $100.00  
  Purchase #6 $112.69   8.788%   $122.5932   $122.59   $122.60   $122.60  
  Purchase #7 $50.37   4.189%   $52.48   $52.48   $52.50   $52.50  
  7 purchase totals = $787.15       $847.1716   $847.17   $847.15   $847.30