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 $49.98   12.495%   $56.225   $56.23   $56.25   $56.20  
  Purchase #2 $176.84   8.437%   $191.76   $191.76   $191.75   $191.80  
  Purchase #3 $47.33   3.818%   $49.1371   $49.14   $49.15   $49.10  
  Purchase #4 $155.27   5.633%   $164.0164   $164.02   $164.00   $164.00  
  Purchase #5 $245.60   7.799%   $264.7543   $264.75   $264.75   $264.80  
  Purchase #6 $216.30   6.808%   $231.0257   $231.03   $231.05   $231.00  
  Purchase #7 $235.61   10.243%   $259.7435   $259.74   $259.75   $259.70  
  7 purchase totals = $1,126.93       $1,216.6620   $1,216.67   $1,216.70   $1,216.60