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 $62.33   5.296%   $65.631   $65.63   $65.65   $65.60  
  Purchase #2 $6.67   10.659%   $7.381   $7.38   $7.40   $7.40  
  Purchase #3 $180.27   3.138%   $185.9269   $185.93   $185.95   $185.90  
  Purchase #4 $111.78   3.447%   $115.6331   $115.63   $115.65   $115.60  
  Purchase #5 $145.86   12.273%   $163.7614   $163.76   $163.75   $163.80  
  Purchase #6 $21.99   9.258%   $24.0258   $24.03   $24.05   $24.00  
  Purchase #7 $226.88   5.328%   $238.9682   $238.97   $238.95   $239.00  
  7 purchase totals = $755.78       $801.3274   $801.33   $801.40   $801.30