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 $41.26   3.595%   $42.7433   $42.74   $42.75   $42.70  
  Purchase #2 $201.96   11.114%   $224.4058   $224.41   $224.40   $224.40  
  Purchase #3 $152.95   5.774%   $161.7813   $161.78   $161.80   $161.80  
  Purchase #4 $229.47   9.442%   $251.1366   $251.14   $251.15   $251.10  
  Purchase #5 $62.34   9.371%   $68.1819   $68.18   $68.20   $68.20  
  Purchase #6 $46.85   3.426%   $48.4551   $48.46   $48.45   $48.50  
  Purchase #7 $221.73   6.598%   $236.3597   $236.36   $236.35   $236.40  
  7 purchase totals = $956.56       $1,033.0637   $1,033.07   $1,033.10   $1,033.10