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 $193.62   7.432%   $208.0098   $208.01   $208.00   $208.00  
  Purchase #2 $108.33   5.667%   $114.4691   $114.47   $114.45   $114.50  
  Purchase #3 $59.86   10.227%   $65.9819   $65.98   $66.00   $66.00  
  Purchase #4 $61.78   11.291%   $68.7556   $68.76   $68.75   $68.80  
  Purchase #5 $68.89   7.805%   $74.2669   $74.27   $74.25   $74.30  
  Purchase #6 $82.94   11.842%   $92.7618   $92.76   $92.75   $92.80  
  Purchase #7 $98.72   11.212%   $109.7885   $109.79   $109.80   $109.80  
  7 purchase totals = $674.14       $734.0336   $734.04   $734.00   $734.20