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 $52.83   12.812%   $59.5986   $59.60   $59.60   $59.60  
  Purchase #2 $23.40   8.798%   $25.4587   $25.46   $25.45   $25.50  
  Purchase #3 $174.99   10.116%   $192.692   $192.69   $192.70   $192.70  
  Purchase #4 $148.92   4.634%   $155.821   $155.82   $155.80   $155.80  
  Purchase #5 $187.60   9.691%   $205.7803   $205.78   $205.80   $205.80  
  Purchase #6 $173.92   11.727%   $194.3156   $194.32   $194.30   $194.30  
  Purchase #7 $148.54   10.291%   $163.8263   $163.83   $163.85   $163.80  
  7 purchase totals = $910.20       $997.4925   $997.50   $997.50   $997.50