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 $67.75   8.734%   $73.6673   $73.67   $73.65   $73.70  
  Purchase #2 $250.61   7.340%   $269.0048   $269.00   $269.00   $269.00  
  Purchase #3 $23.87   8.682%   $25.9424   $25.94   $25.95   $25.90  
  Purchase #4 $59.75   11.102%   $66.3834   $66.38   $66.40   $66.40  
  Purchase #5 $30.64   13.475%   $34.7687   $34.77   $34.75   $34.80  
  Purchase #6 $179.95   6.375%   $191.4218   $191.42   $191.40   $191.40  
  Purchase #7 $163.91   10.510%   $181.1369   $181.14   $181.15   $181.10  
  7 purchase totals = $776.48       $842.3253   $842.32   $842.30   $842.30