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 $150.30   8.874%   $163.6376   $163.64   $163.65   $163.60  
  Purchase #2 $5.93   11.160%   $6.5918   $6.59   $6.60   $6.60  
  Purchase #3 $171.63   11.607%   $191.5511   $191.55   $191.55   $191.60  
  Purchase #4 $23.73   10.162%   $26.1414   $26.14   $26.15   $26.10  
  Purchase #5 $62.81   12.497%   $70.6594   $70.66   $70.65   $70.70  
  Purchase #6 $101.87   13.262%   $115.38   $115.38   $115.40   $115.40  
  Purchase #7 $134.70   12.281%   $151.2425   $151.24   $151.25   $151.20  
  7 purchase totals = $650.97       $725.2038   $725.20   $725.25   $725.20