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 $228.82   10.391%   $252.5967   $252.60   $252.60   $252.60  
  Purchase #2 $63.82   13.356%   $72.3438   $72.34   $72.35   $72.30  
  Purchase #3 $106.69   12.639%   $120.1745   $120.17   $120.15   $120.20  
  Purchase #4 $143.65   13.838%   $163.5283   $163.53   $163.55   $163.50  
  Purchase #5 $24.83   9.183%   $27.1101   $27.11   $27.10   $27.10  
  Purchase #6 $230.86   4.414%   $241.0502   $241.05   $241.05   $241.10  
  Purchase #7 $114.37   8.225%   $123.7769   $123.78   $123.80   $123.80  
  7 purchase totals = $913.04       $1,000.5805   $1,000.58   $1,000.60   $1,000.60