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 $69.52   10.224%   $76.6277   $76.63   $76.65   $76.60  
  Purchase #2 $59.99   6.444%   $63.8558   $63.86   $63.85   $63.90  
  Purchase #3 $109.97   5.403%   $115.9117   $115.91   $115.90   $115.90  
  Purchase #4 $56.91   6.116%   $60.3906   $60.39   $60.40   $60.40  
  Purchase #5 $242.35   7.253%   $259.9276   $259.93   $259.95   $259.90  
  Purchase #6 $93.50   6.566%   $99.6392   $99.64   $99.65   $99.60  
  Purchase #7 $142.45   8.443%   $154.4771   $154.48   $154.50   $154.50  
  7 purchase totals = $774.69       $830.8297   $830.84   $830.90   $830.80