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 $239.68   11.320%   $266.8118   $266.81   $266.80   $266.80  
  Purchase #2 $201.90   13.597%   $229.3523   $229.35   $229.35   $229.40  
  Purchase #3 $99.99   12.828%   $112.8167   $112.82   $112.80   $112.80  
  Purchase #4 $118.39   3.299%   $122.2957   $122.30   $122.30   $122.30  
  Purchase #5 $170.43   6.423%   $181.3767   $181.38   $181.40   $181.40  
  Purchase #6 $15.44   6.566%   $16.4538   $16.45   $16.45   $16.50  
  Purchase #7 $89.79   4.800%   $94.0999   $94.10   $94.10   $94.10  
  7 purchase totals = $935.62       $1,023.2069   $1,023.21   $1,023.20   $1,023.30