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 $77.42   6.574%   $82.5096   $82.51   $82.50   $82.50  
  Purchase #2 $248.62   9.393%   $271.9729   $271.97   $271.95   $272.00  
  Purchase #3 $26.86   13.500%   $30.4861   $30.49   $30.50   $30.50  
  Purchase #4 $122.95   6.208%   $130.5827   $130.58   $130.60   $130.60  
  Purchase #5 $85.73   11.267%   $95.3892   $95.39   $95.40   $95.40  
  Purchase #6 $219.61   12.439%   $246.9273   $246.93   $246.95   $246.90  
  Purchase #7 $153.71   8.363%   $166.5648   $166.56   $166.55   $166.60  
  7 purchase totals = $934.90       $1,024.4326   $1,024.43   $1,024.45   $1,024.50