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 $59.58   3.432%   $61.6248   $61.62   $61.60   $61.60  
  Purchase #2 $165.62   12.468%   $186.2695   $186.27   $186.25   $186.30  
  Purchase #3 $105.66   10.361%   $116.6074   $116.61   $116.60   $116.60  
  Purchase #4 $181.80   12.667%   $204.8286   $204.83   $204.85   $204.80  
  Purchase #5 $161.96   13.330%   $183.5493   $183.55   $183.55   $183.50  
  Purchase #6 $77.81   9.576%   $85.2611   $85.26   $85.25   $85.30  
  Purchase #7 $22.37   8.691%   $24.3142   $24.31   $24.30   $24.30  
  7 purchase totals = $774.80       $862.4549   $862.45   $862.40   $862.40