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 $110.67   11.749%   $123.6726   $123.67   $123.65   $123.70  
  Purchase #2 $22.32   8.855%   $24.2964   $24.30   $24.30   $24.30  
  Purchase #3 $7.67   3.785%   $7.9603   $7.96   $7.95   $8.00  
  Purchase #4 $209.97   3.202%   $216.6932   $216.69   $216.70   $216.70  
  Purchase #5 $107.99   9.871%   $118.6497   $118.65   $118.65   $118.60  
  Purchase #6 $163.84   11.693%   $182.9978   $183.00   $183.00   $183.00  
  Purchase #7 $233.84   9.338%   $255.676   $255.68   $255.70   $255.70  
  7 purchase totals = $856.30       $929.9460   $929.95   $929.95   $930.00