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 $53.34   11.329%   $59.3829   $59.38   $59.40   $59.40  
  Purchase #2 $188.61   11.632%   $210.5491   $210.55   $210.55   $210.50  
  Purchase #3 $243.88   7.471%   $262.1003   $262.10   $262.10   $262.10  
  Purchase #4 $68.99   4.114%   $71.8282   $71.83   $71.85   $71.80  
  Purchase #5 $73.58   7.542%   $79.1294   $79.13   $79.15   $79.10  
  Purchase #6 $74.27   3.264%   $76.6942   $76.69   $76.70   $76.70  
  Purchase #7 $225.41   4.624%   $235.833   $235.83   $235.85   $235.80  
  7 purchase totals = $928.08       $995.5171   $995.51   $995.60   $995.40