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 $93.93   10.534%   $103.8246   $103.82   $103.80   $103.80  
  Purchase #2 $229.30   3.229%   $236.7041   $236.70   $236.70   $236.70  
  Purchase #3 $129.41   3.808%   $134.3379   $134.34   $134.35   $134.30  
  Purchase #4 $206.95   3.337%   $213.8559   $213.86   $213.85   $213.90  
  Purchase #5 $154.75   7.624%   $166.5481   $166.55   $166.55   $166.50  
  Purchase #6 $51.56   11.567%   $57.5239   $57.52   $57.50   $57.50  
  Purchase #7 $69.66   12.855%   $78.6148   $78.61   $78.60   $78.60  
  7 purchase totals = $935.56       $991.4093   $991.40   $991.35   $991.30