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 $20.86   13.366%   $23.6481   $23.65   $23.65   $23.60  
  Purchase #2 $211.38   3.839%   $219.4949   $219.49   $219.50   $219.50  
  Purchase #3 $232.98   4.553%   $243.5876   $243.59   $243.60   $243.60  
  Purchase #4 $124.67   8.228%   $134.9278   $134.93   $134.95   $134.90  
  Purchase #5 $157.81   13.850%   $179.6667   $179.67   $179.65   $179.70  
  Purchase #6 $102.25   3.487%   $105.8155   $105.82   $105.80   $105.80  
  Purchase #7 $101.31   12.554%   $114.0285   $114.03   $114.05   $114.00  
  7 purchase totals = $951.26       $1,021.1691   $1,021.18   $1,021.20   $1,021.10