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 $168.79   9.479%   $184.7896   $184.79   $184.80   $184.80  
  Purchase #2 $6.53   5.626%   $6.8974   $6.90   $6.90   $6.90  
  Purchase #3 $143.70   7.746%   $154.831   $154.83   $154.85   $154.80  
  Purchase #4 $51.71   10.743%   $57.2652   $57.27   $57.25   $57.30  
  Purchase #5 $70.46   4.224%   $73.4362   $73.44   $73.45   $73.40  
  Purchase #6 $122.33   12.324%   $137.4059   $137.41   $137.40   $137.40  
  Purchase #7 $119.50   8.277%   $129.391   $129.39   $129.40   $129.40  
  7 purchase totals = $683.02       $744.0163   $744.03   $744.05   $744.00