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 $223.92   5.466%   $236.1595   $236.16   $236.15   $236.20  
  Purchase #2 $86.91   12.309%   $97.6078   $97.61   $97.60   $97.60  
  Purchase #3 $174.93   12.759%   $197.2493   $197.25   $197.25   $197.20  
  Purchase #4 $245.93   9.215%   $268.5924   $268.59   $268.60   $268.60  
  Purchase #5 $6.41   8.231%   $6.9376   $6.94   $6.95   $6.90  
  Purchase #6 $247.81   9.114%   $270.3954   $270.40   $270.40   $270.40  
  Purchase #7 $148.84   4.790%   $155.9694   $155.97   $155.95   $156.00  
  7 purchase totals = $1,134.75       $1,232.9114   $1,232.92   $1,232.90   $1,232.90