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 $241.61   9.664%   $264.9592   $264.96   $264.95   $265.00  
  Purchase #2 $116.64   13.847%   $132.7911   $132.79   $132.80   $132.80  
  Purchase #3 $159.41   8.579%   $173.0858   $173.09   $173.10   $173.10  
  Purchase #4 $99.31   13.482%   $112.699   $112.70   $112.70   $112.70  
  Purchase #5 $59.96   6.462%   $63.8346   $63.83   $63.85   $63.80  
  Purchase #6 $31.38   9.650%   $34.4082   $34.41   $34.40   $34.40  
  Purchase #7 $218.34   9.710%   $239.5408   $239.54   $239.55   $239.50  
  7 purchase totals = $926.65       $1,021.3187   $1,021.32   $1,021.35   $1,021.30