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 $120.43   3.671%   $124.851   $124.85   $124.85   $124.90  
  Purchase #2 $47.32   4.728%   $49.5573   $49.56   $49.55   $49.60  
  Purchase #3 $182.68   5.231%   $192.236   $192.24   $192.25   $192.20  
  Purchase #4 $69.43   7.332%   $74.5206   $74.52   $74.50   $74.50  
  Purchase #5 $73.61   3.661%   $76.3049   $76.30   $76.30   $76.30  
  Purchase #6 $153.97   6.127%   $163.4037   $163.40   $163.40   $163.40  
  Purchase #7 $242.53   7.175%   $259.9315   $259.93   $259.95   $259.90  
  7 purchase totals = $889.97       $940.8050   $940.80   $940.80   $940.80