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 $199.33   4.484%   $208.268   $208.27   $208.25   $208.30  
  Purchase #2 $43.34   6.211%   $46.0318   $46.03   $46.05   $46.00  
  Purchase #3 $59.81   7.378%   $64.2228   $64.22   $64.20   $64.20  
  Purchase #4 $69.45   3.185%   $71.662   $71.66   $71.65   $71.70  
  Purchase #5 $151.25   9.640%   $165.8305   $165.83   $165.85   $165.80  
  Purchase #6 $49.60   12.336%   $55.7187   $55.72   $55.70   $55.70  
  Purchase #7 $57.95   10.523%   $64.0481   $64.05   $64.05   $64.00  
  7 purchase totals = $630.73       $675.7819   $675.78   $675.75   $675.70