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 $22.59   10.486%   $24.9588   $24.96   $24.95   $25.00  
  Purchase #2 $155.69   7.309%   $167.0694   $167.07   $167.05   $167.10  
  Purchase #3 $52.92   12.410%   $59.4874   $59.49   $59.50   $59.50  
  Purchase #4 $147.95   13.358%   $167.7132   $167.71   $167.70   $167.70  
  Purchase #5 $85.90   13.215%   $97.2517   $97.25   $97.25   $97.30  
  Purchase #6 $65.95   12.427%   $74.1456   $74.15   $74.15   $74.10  
  Purchase #7 $233.36   11.161%   $259.4053   $259.41   $259.40   $259.40  
  7 purchase totals = $764.36       $850.0314   $850.04   $850.00   $850.10