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 $200.63   13.648%   $228.012   $228.01   $228.00   $228.00  
  Purchase #2 $185.92   8.612%   $201.9314   $201.93   $201.95   $201.90  
  Purchase #3 $158.77   6.532%   $169.1409   $169.14   $169.15   $169.10  
  Purchase #4 $194.70   3.421%   $201.3607   $201.36   $201.35   $201.40  
  Purchase #5 $69.87   8.285%   $75.6587   $75.66   $75.65   $75.70  
  Purchase #6 $208.83   8.353%   $226.2736   $226.27   $226.25   $226.30  
  Purchase #7 $166.97   13.624%   $189.718   $189.72   $189.70   $189.70  
  7 purchase totals = $1,185.69       $1,292.0953   $1,292.09   $1,292.05   $1,292.10