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 $226.62   9.846%   $248.933   $248.93   $248.95   $248.90  
  Purchase #2 $61.47   13.277%   $69.6314   $69.63   $69.65   $69.60  
  Purchase #3 $210.61   12.463%   $236.8583   $236.86   $236.85   $236.90  
  Purchase #4 $114.29   11.642%   $127.5956   $127.60   $127.60   $127.60  
  Purchase #5 $211.86   8.482%   $229.83   $229.83   $229.85   $229.80  
  Purchase #6 $8.62   7.643%   $9.2788   $9.28   $9.30   $9.30  
  Purchase #7 $227.99   10.796%   $252.6038   $252.60   $252.60   $252.60  
  7 purchase totals = $1,061.46       $1,174.7309   $1,174.73   $1,174.80   $1,174.70