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 $232.66   12.432%   $261.5843   $261.58   $261.60   $261.60  
  Purchase #2 $134.53   12.572%   $151.4431   $151.44   $151.45   $151.40  
  Purchase #3 $107.37   13.803%   $122.1903   $122.19   $122.20   $122.20  
  Purchase #4 $114.41   6.485%   $121.8295   $121.83   $121.85   $121.80  
  Purchase #5 $49.83   7.131%   $53.3834   $53.38   $53.40   $53.40  
  Purchase #6 $171.82   7.504%   $184.7134   $184.71   $184.70   $184.70  
  Purchase #7 $156.95   12.135%   $175.9959   $176.00   $176.00   $176.00  
  7 purchase totals = $967.57       $1,071.1399   $1,071.13   $1,071.20   $1,071.10