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 $77.65   11.437%   $86.5308   $86.53   $86.55   $86.50  
  Purchase #2 $189.90   3.275%   $196.1192   $196.12   $196.10   $196.10  
  Purchase #3 $21.73   9.308%   $23.7526   $23.75   $23.75   $23.80  
  Purchase #4 $195.33   5.425%   $205.9267   $205.93   $205.95   $205.90  
  Purchase #5 $211.90   12.127%   $237.5971   $237.60   $237.60   $237.60  
  Purchase #6 $65.85   3.587%   $68.212   $68.21   $68.20   $68.20  
  Purchase #7 $248.78   6.536%   $265.0403   $265.04   $265.05   $265.00  
  7 purchase totals = $1,011.14       $1,083.1787   $1,083.18   $1,083.20   $1,083.10