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 $224.91   10.671%   $248.9101   $248.91   $248.90   $248.90  
  Purchase #2 $130.78   11.775%   $146.1793   $146.18   $146.20   $146.20  
  Purchase #3 $186.34   9.248%   $203.5727   $203.57   $203.55   $203.60  
  Purchase #4 $85.76   5.579%   $90.5446   $90.54   $90.55   $90.50  
  Purchase #5 $217.72   13.396%   $246.8858   $246.89   $246.90   $246.90  
  Purchase #6 $114.42   4.461%   $119.5243   $119.52   $119.50   $119.50  
  Purchase #7 $62.82   6.726%   $67.0453   $67.05   $67.05   $67.00  
  7 purchase totals = $1,022.75       $1,122.6621   $1,122.66   $1,122.65   $1,122.60