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 $208.98   12.414%   $234.9228   $234.92   $234.90   $234.90  
  Purchase #2 $152.36   3.282%   $157.3605   $157.36   $157.35   $157.40  
  Purchase #3 $159.30   11.183%   $177.1145   $177.11   $177.10   $177.10  
  Purchase #4 $242.65   6.548%   $258.5387   $258.54   $258.55   $258.50  
  Purchase #5 $197.25   5.755%   $208.6017   $208.60   $208.60   $208.60  
  Purchase #6 $95.49   10.380%   $105.4019   $105.40   $105.40   $105.40  
  Purchase #7 $190.48   6.227%   $202.3412   $202.34   $202.35   $202.30  
  7 purchase totals = $1,246.51       $1,344.2813   $1,344.27   $1,344.25   $1,344.20