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 $95.43   9.327%   $104.3308   $104.33   $104.35   $104.30  
  Purchase #2 $56.92   8.777%   $61.9159   $61.92   $61.90   $61.90  
  Purchase #3 $173.76   3.634%   $180.0744   $180.07   $180.05   $180.10  
  Purchase #4 $109.48   4.865%   $114.8062   $114.81   $114.80   $114.80  
  Purchase #5 $169.45   10.138%   $186.6288   $186.63   $186.65   $186.60  
  Purchase #6 $201.50   3.226%   $208.0004   $208.00   $208.00   $208.00  
  Purchase #7 $55.75   4.541%   $58.2816   $58.28   $58.30   $58.30  
  7 purchase totals = $862.29       $914.0381   $914.04   $914.05   $914.00