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 $185.99   5.471%   $196.1655   $196.17   $196.15   $196.20  
  Purchase #2 $133.73   11.614%   $149.2614   $149.26   $149.25   $149.30  
  Purchase #3 $57.95   9.757%   $63.6042   $63.60   $63.60   $63.60  
  Purchase #4 $71.84   7.250%   $77.0484   $77.05   $77.05   $77.00  
  Purchase #5 $91.72   3.247%   $94.6981   $94.70   $94.70   $94.70  
  Purchase #6 $85.98   11.700%   $96.0397   $96.04   $96.05   $96.00  
  Purchase #7 $116.99   6.686%   $124.812   $124.81   $124.80   $124.80  
  7 purchase totals = $744.20       $801.6293   $801.63   $801.60   $801.60