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 $65.43   11.571%   $73.0009   $73.00   $73.00   $73.00  
  Purchase #2 $132.48   8.430%   $143.6481   $143.65   $143.65   $143.60  
  Purchase #3 $131.86   3.129%   $135.9859   $135.99   $136.00   $136.00  
  Purchase #4 $56.45   13.291%   $63.9528   $63.95   $63.95   $64.00  
  Purchase #5 $79.68   5.402%   $83.9843   $83.98   $84.00   $84.00  
  Purchase #6 $158.45   9.838%   $174.0383   $174.04   $174.05   $174.00  
  Purchase #7 $45.91   13.256%   $51.9958   $52.00   $52.00   $52.00  
  7 purchase totals = $670.26       $726.6061   $726.61   $726.65   $726.60