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 $189.54   10.244%   $208.9565   $208.96   $208.95   $209.00  
  Purchase #2 $66.42   7.764%   $71.5768   $71.58   $71.60   $71.60  
  Purchase #3 $236.78   9.728%   $259.814   $259.81   $259.80   $259.80  
  Purchase #4 $246.91   4.104%   $257.0432   $257.04   $257.05   $257.00  
  Purchase #5 $157.70   3.403%   $163.0665   $163.07   $163.05   $163.10  
  Purchase #6 $107.40   6.738%   $114.6366   $114.64   $114.65   $114.60  
  Purchase #7 $6.53   11.838%   $7.303   $7.30   $7.30   $7.30  
  7 purchase totals = $1,011.28       $1,082.3966   $1,082.40   $1,082.40   $1,082.40