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 $9.36   5.390%   $9.8645   $9.86   $9.85   $9.90  
  Purchase #2 $147.56   9.388%   $161.4129   $161.41   $161.40   $161.40  
  Purchase #3 $189.62   3.696%   $196.6284   $196.63   $196.65   $196.60  
  Purchase #4 $170.91   6.627%   $182.2362   $182.24   $182.25   $182.20  
  Purchase #5 $212.54   7.181%   $227.8025   $227.80   $227.80   $227.80  
  Purchase #6 $83.30   3.608%   $86.3055   $86.31   $86.30   $86.30  
  Purchase #7 $24.61   3.767%   $25.5371   $25.54   $25.55   $25.50  
  7 purchase totals = $837.90       $889.7871   $889.79   $889.80   $889.70