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 $90.73   8.605%   $98.5373   $98.54   $98.55   $98.50  
  Purchase #2 $183.53   5.507%   $193.637   $193.64   $193.65   $193.60  
  Purchase #3 $218.67   9.720%   $239.9247   $239.92   $239.90   $239.90  
  Purchase #4 $229.97   5.268%   $242.0848   $242.08   $242.10   $242.10  
  Purchase #5 $27.26   11.841%   $30.4879   $30.49   $30.50   $30.50  
  Purchase #6 $70.76   11.402%   $78.8281   $78.83   $78.85   $78.80  
  Purchase #7 $73.53   7.121%   $78.7661   $78.77   $78.75   $78.80  
  7 purchase totals = $894.45       $962.2659   $962.27   $962.30   $962.20