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 $242.76   10.238%   $267.6138   $267.61   $267.60   $267.60  
  Purchase #2 $180.66   8.814%   $196.5834   $196.58   $196.60   $196.60  
  Purchase #3 $246.99   4.804%   $258.8554   $258.86   $258.85   $258.90  
  Purchase #4 $161.58   11.239%   $179.74   $179.74   $179.75   $179.70  
  Purchase #5 $164.55   5.719%   $173.9606   $173.96   $173.95   $174.00  
  Purchase #6 $139.66   5.340%   $147.1178   $147.12   $147.10   $147.10  
  Purchase #7 $60.67   12.635%   $68.3357   $68.34   $68.35   $68.30  
  7 purchase totals = $1,196.87       $1,292.2067   $1,292.21   $1,292.20   $1,292.20