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 $63.47   12.246%   $71.2425   $71.24   $71.25   $71.20  
  Purchase #2 $148.96   11.559%   $166.1783   $166.18   $166.20   $166.20  
  Purchase #3 $83.61   13.482%   $94.8823   $94.88   $94.90   $94.90  
  Purchase #4 $218.72   4.724%   $229.0523   $229.05   $229.05   $229.10  
  Purchase #5 $41.58   6.322%   $44.2087   $44.21   $44.20   $44.20  
  Purchase #6 $243.56   3.493%   $252.0676   $252.07   $252.05   $252.10  
  Purchase #7 $101.75   12.229%   $114.193   $114.19   $114.20   $114.20  
  7 purchase totals = $901.65       $971.8247   $971.82   $971.85   $971.90