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 $218.77   8.113%   $236.5188   $236.52   $236.50   $236.50  
  Purchase #2 $101.63   12.820%   $114.659   $114.66   $114.65   $114.70  
  Purchase #3 $78.92   4.523%   $82.4896   $82.49   $82.50   $82.50  
  Purchase #4 $187.46   9.733%   $205.7055   $205.71   $205.70   $205.70  
  Purchase #5 $172.34   3.677%   $178.6769   $178.68   $178.70   $178.70  
  Purchase #6 $115.93   3.133%   $119.5621   $119.56   $119.55   $119.60  
  Purchase #7 $240.96   3.216%   $248.7093   $248.71   $248.70   $248.70  
  7 purchase totals = $1,116.01       $1,186.3212   $1,186.33   $1,186.30   $1,186.40