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 $56.27   4.764%   $58.9507   $58.95   $58.95   $59.00  
  Purchase #2 $151.91   8.666%   $165.0745   $165.07   $165.05   $165.10  
  Purchase #3 $114.80   13.847%   $130.6964   $130.70   $130.70   $130.70  
  Purchase #4 $157.28   9.378%   $172.0297   $172.03   $172.05   $172.00  
  Purchase #5 $125.72   3.554%   $130.1881   $130.19   $130.20   $130.20  
  Purchase #6 $178.81   3.637%   $185.3133   $185.31   $185.30   $185.30  
  Purchase #7 $63.36   8.854%   $68.9699   $68.97   $68.95   $69.00  
  7 purchase totals = $848.15       $911.2226   $911.22   $911.20   $911.30