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 $250.67   6.171%   $266.1388   $266.14   $266.15   $266.10  
  Purchase #2 $59.78   5.693%   $63.1833   $63.18   $63.20   $63.20  
  Purchase #3 $168.40   3.362%   $174.0616   $174.06   $174.05   $174.10  
  Purchase #4 $231.92   6.339%   $246.6214   $246.62   $246.60   $246.60  
  Purchase #5 $135.96   9.223%   $148.4996   $148.50   $148.50   $148.50  
  Purchase #6 $93.48   4.351%   $97.5473   $97.55   $97.55   $97.50  
  Purchase #7 $32.31   3.577%   $33.4657   $33.47   $33.45   $33.50  
  7 purchase totals = $972.52       $1,029.5177   $1,029.52   $1,029.50   $1,029.50