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 $237.95   12.213%   $267.0108   $267.01   $267.00   $267.00  
  Purchase #2 $210.56   7.812%   $227.0089   $227.01   $227.00   $227.00  
  Purchase #3 $134.54   6.734%   $143.5999   $143.60   $143.60   $143.60  
  Purchase #4 $6.68   6.202%   $7.0943   $7.09   $7.10   $7.10  
  Purchase #5 $49.36   13.275%   $55.9125   $55.91   $55.90   $55.90  
  Purchase #6 $64.28   6.565%   $68.5   $68.50   $68.50   $68.50  
  Purchase #7 $24.64   8.855%   $26.8219   $26.82   $26.80   $26.80  
  7 purchase totals = $728.01       $795.9483   $795.94   $795.90   $795.90