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 $106.74   11.598%   $119.1197   $119.12   $119.10   $119.10  
  Purchase #2 $216.69   8.182%   $234.4196   $234.42   $234.40   $234.40  
  Purchase #3 $182.51   8.278%   $197.6182   $197.62   $197.60   $197.60  
  Purchase #4 $221.75   5.834%   $234.6869   $234.69   $234.70   $234.70  
  Purchase #5 $128.63   9.544%   $140.9064   $140.91   $140.90   $140.90  
  Purchase #6 $43.43   5.866%   $45.9776   $45.98   $46.00   $46.00  
  Purchase #7 $81.29   6.809%   $86.825   $86.83   $86.85   $86.80  
  7 purchase totals = $981.04       $1,059.5534   $1,059.57   $1,059.55   $1,059.50