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 $245.95   3.334%   $254.15   $254.15   $254.15   $254.20  
  Purchase #2 $61.53   5.849%   $65.1289   $65.13   $65.15   $65.10  
  Purchase #3 $74.45   4.199%   $77.5762   $77.58   $77.60   $77.60  
  Purchase #4 $19.83   11.761%   $22.1622   $22.16   $22.15   $22.20  
  Purchase #5 $85.63   9.296%   $93.5902   $93.59   $93.60   $93.60  
  Purchase #6 $114.60   7.778%   $123.5136   $123.51   $123.50   $123.50  
  Purchase #7 $185.59   11.588%   $207.0962   $207.10   $207.10   $207.10  
  7 purchase totals = $787.58       $843.2173   $843.22   $843.25   $843.30