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 $98.45   3.670%   $102.0631   $102.06   $102.05   $102.10  
  Purchase #2 $152.97   3.118%   $157.7396   $157.74   $157.75   $157.70  
  Purchase #3 $108.52   9.708%   $119.0551   $119.06   $119.05   $119.10  
  Purchase #4 $160.37   8.261%   $173.6182   $173.62   $173.60   $173.60  
  Purchase #5 $44.99   10.558%   $49.74   $49.74   $49.75   $49.70  
  Purchase #6 $22.31   7.183%   $23.9125   $23.91   $23.90   $23.90  
  Purchase #7 $162.85   3.719%   $168.9064   $168.91   $168.90   $168.90  
  7 purchase totals = $750.46       $795.0349   $795.04   $795.00   $795.00