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 $200.80   13.676%   $228.2614   $228.26   $228.25   $228.30  
  Purchase #2 $69.36   9.830%   $76.1781   $76.18   $76.20   $76.20  
  Purchase #3 $208.73   8.752%   $226.998   $227.00   $227.00   $227.00  
  Purchase #4 $134.44   11.337%   $149.6815   $149.68   $149.70   $149.70  
  Purchase #5 $67.59   6.108%   $71.7184   $71.72   $71.70   $71.70  
  Purchase #6 $233.80   7.566%   $251.4893   $251.49   $251.50   $251.50  
  Purchase #7 $193.55   8.270%   $209.5566   $209.56   $209.55   $209.60  
  7 purchase totals = $1,108.27       $1,213.8833   $1,213.89   $1,213.90   $1,214.00