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 $109.28   5.261%   $115.0292   $115.03   $115.05   $115.00  
  Purchase #2 $232.95   6.620%   $248.3713   $248.37   $248.35   $248.40  
  Purchase #3 $196.78   7.359%   $211.261   $211.26   $211.25   $211.30  
  Purchase #4 $209.63   12.794%   $236.4501   $236.45   $236.45   $236.50  
  Purchase #5 $211.95   7.644%   $228.1515   $228.15   $228.15   $228.20  
  Purchase #6 $176.92   10.379%   $195.2825   $195.28   $195.30   $195.30  
  Purchase #7 $106.65   7.145%   $114.2701   $114.27   $114.25   $114.30  
  7 purchase totals = $1,244.16       $1,348.8157   $1,348.81   $1,348.80   $1,349.00