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 $184.71   11.580%   $206.0994   $206.10   $206.10   $206.10  
  Purchase #2 $21.67   13.582%   $24.6132   $24.61   $24.60   $24.60  
  Purchase #3 $73.78   5.203%   $77.6188   $77.62   $77.60   $77.60  
  Purchase #4 $171.60   9.328%   $187.6068   $187.61   $187.60   $187.60  
  Purchase #5 $156.62   10.336%   $172.8082   $172.81   $172.80   $172.80  
  Purchase #6 $248.30   11.587%   $277.0705   $277.07   $277.05   $277.10  
  Purchase #7 $226.94   6.532%   $241.7637   $241.76   $241.75   $241.80  
  7 purchase totals = $1,083.62       $1,187.5806   $1,187.58   $1,187.50   $1,187.60