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 $52.53   9.670%   $57.6097   $57.61   $57.60   $57.60  
  Purchase #2 $75.86   12.157%   $85.0823   $85.08   $85.10   $85.10  
  Purchase #3 $84.85   5.434%   $89.4607   $89.46   $89.45   $89.50  
  Purchase #4 $122.31   8.774%   $133.0415   $133.04   $133.05   $133.00  
  Purchase #5 $137.81   6.326%   $146.5279   $146.53   $146.55   $146.50  
  Purchase #6 $140.74   5.197%   $148.0543   $148.05   $148.05   $148.10  
  Purchase #7 $13.86   8.297%   $15.01   $15.01   $15.00   $15.00  
  7 purchase totals = $627.96       $674.7864   $674.78   $674.80   $674.80