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 $192.65   9.180%   $210.3353   $210.34   $210.35   $210.30  
  Purchase #2 $52.69   3.256%   $54.4056   $54.41   $54.40   $54.40  
  Purchase #3 $208.34   4.461%   $217.634   $217.63   $217.65   $217.60  
  Purchase #4 $69.76   5.774%   $73.7879   $73.79   $73.80   $73.80  
  Purchase #5 $7.44   4.249%   $7.7561   $7.76   $7.75   $7.80  
  Purchase #6 $223.29   5.126%   $234.7358   $234.74   $234.75   $234.70  
  Purchase #7 $227.90   6.422%   $242.5357   $242.54   $242.55   $242.50  
  7 purchase totals = $982.07       $1,041.1904   $1,041.21   $1,041.25   $1,041.10