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 $67.25   9.305%   $73.5076   $73.51   $73.50   $73.50  
  Purchase #2 $110.87   12.641%   $124.8851   $124.89   $124.90   $124.90  
  Purchase #3 $15.48   11.567%   $17.2706   $17.27   $17.25   $17.30  
  Purchase #4 $221.91   3.250%   $229.1221   $229.12   $229.10   $229.10  
  Purchase #5 $42.78   10.811%   $47.4049   $47.40   $47.40   $47.40  
  Purchase #6 $112.75   10.135%   $124.1772   $124.18   $124.20   $124.20  
  Purchase #7 $122.61   9.555%   $134.3254   $134.33   $134.35   $134.30  
  7 purchase totals = $693.65       $750.6929   $750.70   $750.70   $750.70