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 $79.78   8.154%   $86.2853   $86.29   $86.30   $86.30  
  Purchase #2 $215.50   8.676%   $234.1968   $234.20   $234.20   $234.20  
  Purchase #3 $170.44   7.584%   $183.3662   $183.37   $183.35   $183.40  
  Purchase #4 $202.42   6.566%   $215.7109   $215.71   $215.70   $215.70  
  Purchase #5 $122.53   4.323%   $127.827   $127.83   $127.85   $127.80  
  Purchase #6 $16.66   5.857%   $17.6358   $17.64   $17.65   $17.60  
  Purchase #7 $185.69   8.458%   $201.3957   $201.40   $201.40   $201.40  
  7 purchase totals = $993.02       $1,066.4177   $1,066.44   $1,066.45   $1,066.40