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 $58.50   4.672%   $61.2331   $61.23   $61.25   $61.20  
  Purchase #2 $185.76   11.871%   $207.8116   $207.81   $207.80   $207.80  
  Purchase #3 $173.28   5.783%   $183.3008   $183.30   $183.30   $183.30  
  Purchase #4 $219.81   5.126%   $231.0775   $231.08   $231.10   $231.10  
  Purchase #5 $144.32   5.849%   $152.7613   $152.76   $152.75   $152.80  
  Purchase #6 $40.69   4.793%   $42.6403   $42.64   $42.65   $42.60  
  Purchase #7 $104.50   8.748%   $113.6417   $113.64   $113.65   $113.60  
  7 purchase totals = $926.86       $992.4663   $992.46   $992.50   $992.40