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 $184.97   12.450%   $207.9988   $208.00   $208.00   $208.00  
  Purchase #2 $38.86   7.219%   $41.6653   $41.67   $41.65   $41.70  
  Purchase #3 $79.44   3.383%   $82.1275   $82.13   $82.15   $82.10  
  Purchase #4 $71.78   4.865%   $75.2721   $75.27   $75.25   $75.30  
  Purchase #5 $170.69   4.223%   $177.8982   $177.90   $177.90   $177.90  
  Purchase #6 $165.34   6.577%   $176.2144   $176.21   $176.20   $176.20  
  Purchase #7 $219.71   3.809%   $228.0788   $228.08   $228.10   $228.10  
  7 purchase totals = $930.79       $989.2551   $989.26   $989.25   $989.30