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 $244.65   13.194%   $276.9291   $276.93   $276.95   $276.90  
  Purchase #2 $209.68   12.548%   $235.9906   $235.99   $236.00   $236.00  
  Purchase #3 $61.48   3.819%   $63.8279   $63.83   $63.85   $63.80  
  Purchase #4 $212.59   12.836%   $239.8781   $239.88   $239.90   $239.90  
  Purchase #5 $160.45   4.641%   $167.8965   $167.90   $167.90   $167.90  
  Purchase #6 $44.61   11.365%   $49.6799   $49.68   $49.70   $49.70  
  Purchase #7 $167.85   5.444%   $176.9878   $176.99   $177.00   $177.00  
  7 purchase totals = $1,101.31       $1,211.1899   $1,211.20   $1,211.30   $1,211.20