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 $212.53   6.462%   $226.2637   $226.26   $226.25   $226.30  
  Purchase #2 $21.83   10.209%   $24.0586   $24.06   $24.05   $24.10  
  Purchase #3 $65.48   7.518%   $70.4028   $70.40   $70.40   $70.40  
  Purchase #4 $84.34   13.703%   $95.8971   $95.90   $95.90   $95.90  
  Purchase #5 $98.91   12.579%   $111.3519   $111.35   $111.35   $111.40  
  Purchase #6 $16.93   5.851%   $17.9206   $17.92   $17.90   $17.90  
  Purchase #7 $238.26   10.365%   $262.9556   $262.96   $262.95   $263.00  
  7 purchase totals = $738.28       $808.8503   $808.85   $808.80   $809.00