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 $78.73   5.289%   $82.894   $82.89   $82.90   $82.90  
  Purchase #2 $123.28   8.309%   $133.5233   $133.52   $133.50   $133.50  
  Purchase #3 $32.52   5.765%   $34.3948   $34.39   $34.40   $34.40  
  Purchase #4 $241.66   7.420%   $259.5912   $259.59   $259.60   $259.60  
  Purchase #5 $192.33   8.742%   $209.1435   $209.14   $209.15   $209.10  
  Purchase #6 $107.88   5.134%   $113.4186   $113.42   $113.40   $113.40  
  Purchase #7 $144.63   7.345%   $155.2531   $155.25   $155.25   $155.30  
  7 purchase totals = $921.03       $988.2185   $988.20   $988.20   $988.20