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 $94.27   4.271%   $98.2963   $98.30   $98.30   $98.30  
  Purchase #2 $169.59   9.653%   $185.9605   $185.96   $185.95   $186.00  
  Purchase #3 $65.80   13.160%   $74.4593   $74.46   $74.45   $74.50  
  Purchase #4 $81.55   5.848%   $86.319   $86.32   $86.30   $86.30  
  Purchase #5 $153.61   6.829%   $164.1   $164.10   $164.10   $164.10  
  Purchase #6 $120.60   11.278%   $134.2013   $134.20   $134.20   $134.20  
  Purchase #7 $243.37   12.432%   $273.6258   $273.63   $273.65   $273.60  
  7 purchase totals = $928.79       $1,016.9622   $1,016.97   $1,016.95   $1,017.00