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 $186.25   8.110%   $201.3549   $201.35   $201.35   $201.40  
  Purchase #2 $134.88   10.373%   $148.8711   $148.87   $148.85   $148.90  
  Purchase #3 $22.33   8.188%   $24.1584   $24.16   $24.15   $24.20  
  Purchase #4 $224.46   3.142%   $231.5125   $231.51   $231.50   $231.50  
  Purchase #5 $48.42   8.135%   $52.359   $52.36   $52.35   $52.40  
  Purchase #6 $164.36   7.838%   $177.2425   $177.24   $177.25   $177.20  
  Purchase #7 $228.30   12.118%   $255.9654   $255.97   $255.95   $256.00  
  7 purchase totals = $1,009.00       $1,091.4638   $1,091.46   $1,091.40   $1,091.60