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 $122.46   6.379%   $130.2717   $130.27   $130.25   $130.30  
  Purchase #2 $208.85   13.211%   $236.4412   $236.44   $236.45   $236.40  
  Purchase #3 $69.51   7.281%   $74.571   $74.57   $74.55   $74.60  
  Purchase #4 $115.55   9.695%   $126.7526   $126.75   $126.75   $126.80  
  Purchase #5 $172.60   8.580%   $187.4091   $187.41   $187.40   $187.40  
  Purchase #6 $224.67   3.674%   $232.9244   $232.92   $232.90   $232.90  
  Purchase #7 $42.32   13.246%   $47.9257   $47.93   $47.95   $47.90  
  7 purchase totals = $955.96       $1,036.2957   $1,036.29   $1,036.25   $1,036.30