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 $40.86   13.525%   $46.3863   $46.39   $46.40   $46.40  
  Purchase #2 $223.66   12.824%   $252.3422   $252.34   $252.35   $252.30  
  Purchase #3 $202.44   12.737%   $228.2248   $228.22   $228.20   $228.20  
  Purchase #4 $130.49   5.171%   $137.2376   $137.24   $137.25   $137.20  
  Purchase #5 $248.50   3.866%   $258.107   $258.11   $258.10   $258.10  
  Purchase #6 $143.26   12.737%   $161.507   $161.51   $161.50   $161.50  
  Purchase #7 $135.89   11.490%   $151.5038   $151.50   $151.50   $151.50  
  7 purchase totals = $1,125.10       $1,235.3087   $1,235.31   $1,235.30   $1,235.20