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 $84.81   9.120%   $92.5447   $92.54   $92.55   $92.50  
  Purchase #2 $228.89   10.359%   $252.6007   $252.60   $252.60   $252.60  
  Purchase #3 $155.59   13.382%   $176.4111   $176.41   $176.40   $176.40  
  Purchase #4 $91.57   7.107%   $98.0779   $98.08   $98.10   $98.10  
  Purchase #5 $213.45   12.268%   $239.636   $239.64   $239.65   $239.60  
  Purchase #6 $132.89   6.630%   $141.7006   $141.70   $141.70   $141.70  
  Purchase #7 $130.52   7.709%   $140.5818   $140.58   $140.60   $140.60  
  7 purchase totals = $1,037.72       $1,141.5528   $1,141.55   $1,141.60   $1,141.50