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 $35.92   4.678%   $37.6003   $37.60   $37.60   $37.60  
  Purchase #2 $242.41   8.649%   $263.376   $263.38   $263.40   $263.40  
  Purchase #3 $122.81   8.666%   $133.4527   $133.45   $133.45   $133.50  
  Purchase #4 $165.64   6.455%   $176.3321   $176.33   $176.35   $176.30  
  Purchase #5 $106.59   3.226%   $110.0286   $110.03   $110.05   $110.00  
  Purchase #6 $130.60   7.359%   $140.2109   $140.21   $140.20   $140.20  
  Purchase #7 $127.96   5.626%   $135.159   $135.16   $135.15   $135.20  
  7 purchase totals = $931.93       $996.1596   $996.16   $996.20   $996.20