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 $210.58   11.608%   $235.0241   $235.02   $235.00   $235.00  
  Purchase #2 $151.59   5.816%   $160.4065   $160.41   $160.40   $160.40  
  Purchase #3 $83.47   13.585%   $94.8094   $94.81   $94.80   $94.80  
  Purchase #4 $219.46   7.852%   $236.692   $236.69   $236.70   $236.70  
  Purchase #5 $114.45   13.145%   $129.4945   $129.49   $129.50   $129.50  
  Purchase #6 $63.42   3.244%   $65.4773   $65.48   $65.50   $65.50  
  Purchase #7 $162.63   7.162%   $174.2776   $174.28   $174.30   $174.30  
  7 purchase totals = $1,005.60       $1,096.1814   $1,096.18   $1,096.20   $1,096.20