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 $242.49   10.271%   $267.3961   $267.40   $267.40   $267.40  
  Purchase #2 $80.68   8.226%   $87.3167   $87.32   $87.30   $87.30  
  Purchase #3 $123.37   10.273%   $136.0438   $136.04   $136.05   $136.00  
  Purchase #4 $60.89   11.346%   $67.7986   $67.80   $67.80   $67.80  
  Purchase #5 $201.42   8.269%   $218.0754   $218.08   $218.10   $218.10  
  Purchase #6 $71.59   8.648%   $77.7811   $77.78   $77.80   $77.80  
  Purchase #7 $155.65   11.326%   $173.2789   $173.28   $173.30   $173.30  
  7 purchase totals = $936.09       $1,027.6906   $1,027.70   $1,027.75   $1,027.70