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 $62.33   8.454%   $67.5994   $67.60   $67.60   $67.60  
  Purchase #2 $123.42   3.133%   $127.2867   $127.29   $127.30   $127.30  
  Purchase #3 $236.60   9.325%   $258.663   $258.66   $258.65   $258.70  
  Purchase #4 $230.79   13.167%   $261.1781   $261.18   $261.20   $261.20  
  Purchase #5 $186.67   12.436%   $209.8843   $209.88   $209.90   $209.90  
  Purchase #6 $20.54   11.718%   $22.9469   $22.95   $22.95   $22.90  
  Purchase #7 $43.83   10.362%   $48.3717   $48.37   $48.35   $48.40  
  7 purchase totals = $904.18       $995.9301   $995.93   $995.95   $996.00