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 $41.87   3.859%   $43.4858   $43.49   $43.50   $43.50  
  Purchase #2 $171.65   13.660%   $195.0974   $195.10   $195.10   $195.10  
  Purchase #3 $247.75   3.686%   $256.8821   $256.88   $256.90   $256.90  
  Purchase #4 $195.44   5.838%   $206.8498   $206.85   $206.85   $206.80  
  Purchase #5 $68.54   10.373%   $75.6497   $75.65   $75.65   $75.60  
  Purchase #6 $217.28   5.225%   $228.6329   $228.63   $228.65   $228.60  
  Purchase #7 $215.32   6.566%   $229.4579   $229.46   $229.45   $229.50  
  7 purchase totals = $1,157.85       $1,236.0556   $1,236.06   $1,236.10   $1,236.00