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 $186.88   3.631%   $193.6656   $193.67   $193.65   $193.70  
  Purchase #2 $119.95   11.592%   $133.8546   $133.85   $133.85   $133.90  
  Purchase #3 $176.43   4.540%   $184.4399   $184.44   $184.45   $184.40  
  Purchase #4 $92.75   5.479%   $97.8318   $97.83   $97.85   $97.80  
  Purchase #5 $246.68   4.515%   $257.8176   $257.82   $257.80   $257.80  
  Purchase #6 $7.35   6.296%   $7.8128   $7.81   $7.80   $7.80  
  Purchase #7 $130.89   11.682%   $146.1806   $146.18   $146.20   $146.20  
  7 purchase totals = $960.93       $1,021.6029   $1,021.60   $1,021.60   $1,021.60