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 $206.93   9.228%   $226.0255   $226.03   $226.05   $226.00  
  Purchase #2 $119.53   13.636%   $135.8291   $135.83   $135.85   $135.80  
  Purchase #3 $87.45   10.239%   $96.404   $96.40   $96.40   $96.40  
  Purchase #4 $121.63   10.658%   $134.5933   $134.59   $134.60   $134.60  
  Purchase #5 $222.80   13.723%   $253.3748   $253.37   $253.35   $253.40  
  Purchase #6 $98.32   6.268%   $104.4827   $104.48   $104.50   $104.50  
  Purchase #7 $62.62   12.331%   $70.3417   $70.34   $70.35   $70.30  
  7 purchase totals = $919.28       $1,021.0511   $1,021.04   $1,021.10   $1,021.00