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 $24.26   9.689%   $26.6106   $26.61   $26.60   $26.60  
  Purchase #2 $50.87   13.334%   $57.653   $57.65   $57.65   $57.70  
  Purchase #3 $95.68   12.301%   $107.4496   $107.45   $107.45   $107.40  
  Purchase #4 $55.87   3.580%   $57.8701   $57.87   $57.85   $57.90  
  Purchase #5 $173.67   12.679%   $195.6896   $195.69   $195.70   $195.70  
  Purchase #6 $223.28   5.306%   $235.1272   $235.13   $235.15   $235.10  
  Purchase #7 $105.26   10.631%   $116.4502   $116.45   $116.45   $116.50  
  7 purchase totals = $728.89       $796.8503   $796.85   $796.85   $796.90