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 $64.26   11.742%   $71.8054   $71.81   $71.80   $71.80  
  Purchase #2 $203.73   13.367%   $230.9626   $230.96   $230.95   $231.00  
  Purchase #3 $243.88   12.323%   $273.9333   $273.93   $273.95   $273.90  
  Purchase #4 $175.96   13.175%   $199.1427   $199.14   $199.15   $199.10  
  Purchase #5 $50.42   11.543%   $56.24   $56.24   $56.25   $56.20  
  Purchase #6 $111.92   7.151%   $119.9234   $119.92   $119.90   $119.90  
  Purchase #7 $199.88   4.405%   $208.6847   $208.68   $208.70   $208.70  
  7 purchase totals = $1,050.05       $1,160.6921   $1,160.68   $1,160.70   $1,160.60