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 $22.56   11.225%   $25.0924   $25.09   $25.10   $25.10  
  Purchase #2 $193.32   6.306%   $205.5108   $205.51   $205.50   $205.50  
  Purchase #3 $61.34   8.434%   $66.5134   $66.51   $66.50   $66.50  
  Purchase #4 $201.92   3.461%   $208.9085   $208.91   $208.90   $208.90  
  Purchase #5 $124.79   8.403%   $135.2761   $135.28   $135.30   $135.30  
  Purchase #6 $245.69   11.107%   $272.9788   $272.98   $273.00   $273.00  
  Purchase #7 $82.46   10.846%   $91.4036   $91.40   $91.40   $91.40  
  7 purchase totals = $932.08       $1,005.6836   $1,005.68   $1,005.70   $1,005.70