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 $164.48   11.623%   $183.5975   $183.60   $183.60   $183.60  
  Purchase #2 $224.42   10.799%   $248.6551   $248.66   $248.65   $248.70  
  Purchase #3 $19.42   8.442%   $21.0594   $21.06   $21.05   $21.10  
  Purchase #4 $160.50   7.240%   $172.1202   $172.12   $172.10   $172.10  
  Purchase #5 $175.54   10.818%   $194.5299   $194.53   $194.55   $194.50  
  Purchase #6 $160.99   9.117%   $175.6675   $175.67   $175.65   $175.70  
  Purchase #7 $246.46   6.519%   $262.5267   $262.53   $262.55   $262.50  
  7 purchase totals = $1,151.81       $1,258.1563   $1,258.17   $1,258.15   $1,258.20