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 $157.34   5.471%   $165.9481   $165.95   $165.95   $165.90  
  Purchase #2 $73.69   11.621%   $82.2535   $82.25   $82.25   $82.30  
  Purchase #3 $198.88   7.295%   $213.3883   $213.39   $213.40   $213.40  
  Purchase #4 $43.66   10.698%   $48.3307   $48.33   $48.35   $48.30  
  Purchase #5 $231.33   9.825%   $254.0582   $254.06   $254.05   $254.10  
  Purchase #6 $35.50   8.785%   $38.6187   $38.62   $38.60   $38.60  
  Purchase #7 $174.81   11.206%   $194.3992   $194.40   $194.40   $194.40  
  7 purchase totals = $915.21       $996.9967   $997.00   $997.00   $997.00