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 $113.42   12.353%   $127.4308   $127.43   $127.45   $127.40  
  Purchase #2 $153.46   8.791%   $166.9507   $166.95   $166.95   $167.00  
  Purchase #3 $157.62   6.326%   $167.591   $167.59   $167.60   $167.60  
  Purchase #4 $207.32   9.636%   $227.2974   $227.30   $227.30   $227.30  
  Purchase #5 $228.52   6.757%   $243.9611   $243.96   $243.95   $244.00  
  Purchase #6 $111.99   3.498%   $115.9074   $115.91   $115.90   $115.90  
  Purchase #7 $50.60   9.758%   $55.5375   $55.54   $55.55   $55.50  
  7 purchase totals = $1,022.93       $1,104.6759   $1,104.68   $1,104.70   $1,104.70