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 $237.83   13.243%   $269.3258   $269.33   $269.35   $269.30  
  Purchase #2 $148.66   4.195%   $154.8963   $154.90   $154.90   $154.90  
  Purchase #3 $204.28   4.347%   $213.1601   $213.16   $213.15   $213.20  
  Purchase #4 $220.80   6.684%   $235.5583   $235.56   $235.55   $235.60  
  Purchase #5 $212.36   6.152%   $225.4244   $225.42   $225.40   $225.40  
  Purchase #6 $191.68   5.632%   $202.4754   $202.48   $202.50   $202.50  
  Purchase #7 $26.99   11.696%   $30.1468   $30.15   $30.15   $30.10  
  7 purchase totals = $1,242.60       $1,330.9871   $1,331.00   $1,331.00   $1,331.00