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 $214.51   13.190%   $242.8039   $242.80   $242.80   $242.80  
  Purchase #2 $52.72   7.106%   $56.4663   $56.47   $56.45   $56.50  
  Purchase #3 $234.59   9.817%   $257.6197   $257.62   $257.60   $257.60  
  Purchase #4 $18.92   10.850%   $20.9728   $20.97   $20.95   $21.00  
  Purchase #5 $248.78   8.238%   $269.2745   $269.27   $269.25   $269.30  
  Purchase #6 $242.76   12.692%   $273.5711   $273.57   $273.55   $273.60  
  Purchase #7 $101.45   4.647%   $106.1644   $106.16   $106.15   $106.20  
  7 purchase totals = $1,113.73       $1,226.8727   $1,226.86   $1,226.75   $1,227.00