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 $220.26   9.427%   $241.0239   $241.02   $241.00   $241.00  
  Purchase #2 $13.80   10.564%   $15.2578   $15.26   $15.25   $15.30  
  Purchase #3 $236.54   6.743%   $252.4899   $252.49   $252.50   $252.50  
  Purchase #4 $100.83   4.433%   $105.2998   $105.30   $105.30   $105.30  
  Purchase #5 $24.38   8.515%   $26.456   $26.46   $26.45   $26.50  
  Purchase #6 $50.78   9.862%   $55.7879   $55.79   $55.80   $55.80  
  Purchase #7 $122.57   3.332%   $126.654   $126.65   $126.65   $126.70  
  7 purchase totals = $769.16       $822.9693   $822.97   $822.95   $823.10