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 $87.44   10.114%   $96.2837   $96.28   $96.30   $96.30  
  Purchase #2 $91.48   6.609%   $97.5259   $97.53   $97.55   $97.50  
  Purchase #3 $240.86   13.419%   $273.181   $273.18   $273.20   $273.20  
  Purchase #4 $175.98   5.855%   $186.2836   $186.28   $186.30   $186.30  
  Purchase #5 $188.47   10.273%   $207.8315   $207.83   $207.85   $207.80  
  Purchase #6 $148.66   9.723%   $163.1142   $163.11   $163.10   $163.10  
  Purchase #7 $16.78   12.808%   $18.9292   $18.93   $18.95   $18.90  
  7 purchase totals = $949.67       $1,043.1491   $1,043.14   $1,043.25   $1,043.10