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 $216.63   13.771%   $246.4621   $246.46   $246.45   $246.50  
  Purchase #2 $222.29   8.239%   $240.6045   $240.60   $240.60   $240.60  
  Purchase #3 $95.81   5.613%   $101.1878   $101.19   $101.20   $101.20  
  Purchase #4 $16.78   11.804%   $18.7607   $18.76   $18.75   $18.80  
  Purchase #5 $202.38   13.229%   $229.1529   $229.15   $229.15   $229.20  
  Purchase #6 $223.45   8.201%   $241.7751   $241.78   $241.80   $241.80  
  Purchase #7 $114.65   7.222%   $122.93   $122.93   $122.95   $122.90  
  7 purchase totals = $1,091.99       $1,200.8731   $1,200.87   $1,200.90   $1,201.00