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 $232.73   5.592%   $245.7443   $245.74   $245.75   $245.70  
  Purchase #2 $242.56   13.832%   $276.1109   $276.11   $276.10   $276.10  
  Purchase #3 $215.32   5.249%   $226.6221   $226.62   $226.60   $226.60  
  Purchase #4 $9.25   11.188%   $10.2849   $10.28   $10.30   $10.30  
  Purchase #5 $84.46   6.420%   $89.8823   $89.88   $89.90   $89.90  
  Purchase #6 $35.68   8.497%   $38.7117   $38.71   $38.70   $38.70  
  Purchase #7 $129.99   4.261%   $135.5289   $135.53   $135.55   $135.50  
  7 purchase totals = $949.99       $1,022.8851   $1,022.87   $1,022.90   $1,022.80