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 $163.76   5.789%   $173.2401   $173.24   $173.25   $173.20  
  Purchase #2 $76.26   8.814%   $82.9816   $82.98   $83.00   $83.00  
  Purchase #3 $47.94   5.873%   $50.7555   $50.76   $50.75   $50.80  
  Purchase #4 $81.39   13.417%   $92.3101   $92.31   $92.30   $92.30  
  Purchase #5 $90.58   13.109%   $102.4541   $102.45   $102.45   $102.50  
  Purchase #6 $71.50   8.815%   $77.8027   $77.80   $77.80   $77.80  
  Purchase #7 $15.28   11.792%   $17.0818   $17.08   $17.10   $17.10  
  7 purchase totals = $546.71       $596.6259   $596.62   $596.65   $596.70