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 $242.69   10.553%   $268.3011   $268.30   $268.30   $268.30  
  Purchase #2 $63.51   4.112%   $66.1215   $66.12   $66.10   $66.10  
  Purchase #3 $183.44   5.307%   $193.1752   $193.18   $193.20   $193.20  
  Purchase #4 $63.76   12.198%   $71.5374   $71.54   $71.55   $71.50  
  Purchase #5 $235.59   11.746%   $263.2624   $263.26   $263.25   $263.30  
  Purchase #6 $157.57   11.676%   $175.9679   $175.97   $175.95   $176.00  
  Purchase #7 $152.79   8.208%   $165.331   $165.33   $165.35   $165.30  
  7 purchase totals = $1,099.35       $1,203.6965   $1,203.70   $1,203.70   $1,203.70