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 $32.92   4.684%   $34.462   $34.46   $34.45   $34.50  
  Purchase #2 $119.59   3.274%   $123.5054   $123.51   $123.50   $123.50  
  Purchase #3 $118.68   6.112%   $125.9337   $125.93   $125.95   $125.90  
  Purchase #4 $21.64   11.104%   $24.0429   $24.04   $24.05   $24.00  
  Purchase #5 $149.35   4.193%   $155.6122   $155.61   $155.60   $155.60  
  Purchase #6 $246.88   8.809%   $268.6277   $268.63   $268.65   $268.60  
  Purchase #7 $248.88   5.710%   $263.091   $263.09   $263.10   $263.10  
  7 purchase totals = $937.94       $995.2749   $995.27   $995.30   $995.20