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 $191.61   7.852%   $206.6552   $206.66   $206.65   $206.70  
  Purchase #2 $212.67   10.522%   $235.0471   $235.05   $235.05   $235.00  
  Purchase #3 $8.81   8.419%   $9.5517   $9.55   $9.55   $9.60  
  Purchase #4 $105.34   13.424%   $119.4808   $119.48   $119.50   $119.50  
  Purchase #5 $226.58   4.134%   $235.9468   $235.95   $235.95   $235.90  
  Purchase #6 $36.59   10.227%   $40.3321   $40.33   $40.35   $40.30  
  Purchase #7 $68.87   6.863%   $73.5965   $73.60   $73.60   $73.60  
  7 purchase totals = $850.47       $920.6102   $920.62   $920.65   $920.60