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 $61.69   12.579%   $69.45   $69.45   $69.45   $69.50  
  Purchase #2 $79.48   6.114%   $84.3394   $84.34   $84.35   $84.30  
  Purchase #3 $43.45   11.592%   $48.4867   $48.49   $48.50   $48.50  
  Purchase #4 $197.25   3.448%   $204.0512   $204.05   $204.05   $204.10  
  Purchase #5 $153.40   7.820%   $165.3959   $165.40   $165.40   $165.40  
  Purchase #6 $38.38   5.440%   $40.4679   $40.47   $40.45   $40.50  
  Purchase #7 $102.90   12.438%   $115.6987   $115.70   $115.70   $115.70  
  7 purchase totals = $676.55       $727.8898   $727.90   $727.90   $728.00