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 $90.97   6.223%   $96.6311   $96.63   $96.65   $96.60  
  Purchase #2 $125.69   12.254%   $141.0921   $141.09   $141.10   $141.10  
  Purchase #3 $130.98   6.369%   $139.3221   $139.32   $139.30   $139.30  
  Purchase #4 $94.33   8.254%   $102.116   $102.12   $102.10   $102.10  
  Purchase #5 $171.69   12.765%   $193.6062   $193.61   $193.60   $193.60  
  Purchase #6 $161.47   7.304%   $173.2638   $173.26   $173.25   $173.30  
  Purchase #7 $104.82   9.704%   $114.9917   $114.99   $115.00   $115.00  
  7 purchase totals = $879.95       $961.0230   $961.02   $961.00   $961.00