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 $227.82   9.139%   $248.6405   $248.64   $248.65   $248.60  
  Purchase #2 $65.37   11.759%   $73.0569   $73.06   $73.05   $73.10  
  Purchase #3 $98.81   5.750%   $104.4916   $104.49   $104.50   $104.50  
  Purchase #4 $115.30   5.708%   $121.8813   $121.88   $121.90   $121.90  
  Purchase #5 $62.41   10.565%   $69.0036   $69.00   $69.00   $69.00  
  Purchase #6 $178.41   5.150%   $187.5981   $187.60   $187.60   $187.60  
  Purchase #7 $192.59   4.568%   $201.3875   $201.39   $201.40   $201.40  
  7 purchase totals = $940.71       $1,006.0595   $1,006.06   $1,006.10   $1,006.10