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 $248.63   11.661%   $277.6227   $277.62   $277.60   $277.60  
  Purchase #2 $156.91   13.368%   $177.8857   $177.89   $177.90   $177.90  
  Purchase #3 $209.58   8.426%   $227.2392   $227.24   $227.25   $227.20  
  Purchase #4 $69.41   12.373%   $77.9981   $78.00   $78.00   $78.00  
  Purchase #5 $61.82   8.544%   $67.1019   $67.10   $67.10   $67.10  
  Purchase #6 $145.49   10.448%   $160.6908   $160.69   $160.70   $160.70  
  Purchase #7 $96.53   10.376%   $106.546   $106.55   $106.55   $106.50  
  7 purchase totals = $988.37       $1,095.0844   $1,095.09   $1,095.10   $1,095.00