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 $233.87   8.801%   $254.4529   $254.45   $254.45   $254.50  
  Purchase #2 $61.85   5.347%   $65.1571   $65.16   $65.15   $65.20  
  Purchase #3 $152.65   12.320%   $171.4565   $171.46   $171.45   $171.50  
  Purchase #4 $90.56   5.382%   $95.4339   $95.43   $95.45   $95.40  
  Purchase #5 $141.81   10.429%   $156.5994   $156.60   $156.60   $156.60  
  Purchase #6 $120.60   12.637%   $135.8402   $135.84   $135.85   $135.80  
  Purchase #7 $151.59   3.693%   $157.1882   $157.19   $157.20   $157.20  
  7 purchase totals = $952.93       $1,036.1282   $1,036.13   $1,036.15   $1,036.20