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 $41.51   11.347%   $46.2201   $46.22   $46.20   $46.20  
  Purchase #2 $220.92   6.797%   $235.9359   $235.94   $235.95   $235.90  
  Purchase #3 $35.46   9.465%   $38.8163   $38.82   $38.80   $38.80  
  Purchase #4 $242.71   3.453%   $251.0908   $251.09   $251.10   $251.10  
  Purchase #5 $158.99   3.118%   $163.9473   $163.95   $163.95   $163.90  
  Purchase #6 $29.92   3.587%   $30.9932   $30.99   $31.00   $31.00  
  Purchase #7 $229.84   5.436%   $242.3341   $242.33   $242.35   $242.30  
  7 purchase totals = $959.35       $1,009.3377   $1,009.34   $1,009.35   $1,009.20