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 $197.94   10.615%   $218.9513   $218.95   $218.95   $219.00  
  Purchase #2 $216.67   9.170%   $236.5386   $236.54   $236.55   $236.50  
  Purchase #3 $180.78   7.203%   $193.8016   $193.80   $193.80   $193.80  
  Purchase #4 $144.53   8.564%   $156.9075   $156.91   $156.90   $156.90  
  Purchase #5 $238.53   6.182%   $253.2759   $253.28   $253.30   $253.30  
  Purchase #6 $229.31   3.195%   $236.6365   $236.64   $236.65   $236.60  
  Purchase #7 $59.83   7.651%   $64.4076   $64.41   $64.40   $64.40  
  7 purchase totals = $1,267.59       $1,360.5190   $1,360.53   $1,360.55   $1,360.50