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 $52.35   12.271%   $58.7739   $58.77   $58.75   $58.80  
  Purchase #2 $123.46   11.478%   $137.6307   $137.63   $137.65   $137.60  
  Purchase #3 $195.66   5.359%   $206.1454   $206.15   $206.15   $206.10  
  Purchase #4 $65.90   8.597%   $71.5654   $71.57   $71.55   $71.60  
  Purchase #5 $208.99   12.215%   $234.5181   $234.52   $234.50   $234.50  
  Purchase #6 $61.33   7.154%   $65.7175   $65.72   $65.70   $65.70  
  Purchase #7 $7.81   10.114%   $8.5999   $8.60   $8.60   $8.60  
  7 purchase totals = $715.50       $782.9509   $782.96   $782.90   $782.90