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 $61.81   3.439%   $63.9356   $63.94   $63.95   $63.90  
  Purchase #2 $84.81   8.132%   $91.7067   $91.71   $91.70   $91.70  
  Purchase #3 $69.92   8.564%   $75.9079   $75.91   $75.90   $75.90  
  Purchase #4 $57.44   13.632%   $65.2702   $65.27   $65.25   $65.30  
  Purchase #5 $92.40   12.266%   $103.7338   $103.73   $103.75   $103.70  
  Purchase #6 $225.73   8.210%   $244.2624   $244.26   $244.25   $244.30  
  Purchase #7 $216.46   3.201%   $223.3889   $223.39   $223.40   $223.40  
  7 purchase totals = $808.57       $868.2055   $868.21   $868.20   $868.20