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 $136.80   3.212%   $141.194   $141.19   $141.20   $141.20  
  Purchase #2 $96.52   11.771%   $107.8814   $107.88   $107.90   $107.90  
  Purchase #3 $75.49   10.834%   $83.6686   $83.67   $83.65   $83.70  
  Purchase #4 $208.57   13.187%   $236.0741   $236.07   $236.05   $236.10  
  Purchase #5 $124.36   11.831%   $139.073   $139.07   $139.05   $139.10  
  Purchase #6 $97.25   11.149%   $108.0924   $108.09   $108.10   $108.10  
  Purchase #7 $199.52   4.502%   $208.5024   $208.50   $208.50   $208.50  
  7 purchase totals = $938.51       $1,024.4859   $1,024.47   $1,024.45   $1,024.60