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 $56.67   4.393%   $59.1595   $59.16   $59.15   $59.20  
  Purchase #2 $109.76   11.109%   $121.9532   $121.95   $121.95   $122.00  
  Purchase #3 $54.80   4.265%   $57.1372   $57.14   $57.15   $57.10  
  Purchase #4 $185.84   5.831%   $196.6763   $196.68   $196.70   $196.70  
  Purchase #5 $179.41   7.636%   $193.1097   $193.11   $193.10   $193.10  
  Purchase #6 $84.93   13.724%   $96.5858   $96.59   $96.60   $96.60  
  Purchase #7 $223.77   4.128%   $233.0072   $233.01   $233.00   $233.00  
  7 purchase totals = $895.18       $957.6289   $957.64   $957.65   $957.70