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 $92.72   6.116%   $98.3908   $98.39   $98.40   $98.40  
  Purchase #2 $179.44   8.489%   $194.6727   $194.67   $194.65   $194.70  
  Purchase #3 $250.73   7.574%   $269.7203   $269.72   $269.70   $269.70  
  Purchase #4 $235.71   9.675%   $258.5149   $258.51   $258.50   $258.50  
  Purchase #5 $205.80   13.742%   $234.081   $234.08   $234.10   $234.10  
  Purchase #6 $18.36   13.633%   $20.863   $20.86   $20.85   $20.90  
  Purchase #7 $116.41   11.383%   $129.661   $129.66   $129.65   $129.70  
  7 purchase totals = $1,099.17       $1,205.9037   $1,205.89   $1,205.85   $1,206.00