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 $248.72   5.843%   $263.2527   $263.25   $263.25   $263.30  
  Purchase #2 $201.61   13.411%   $228.6479   $228.65   $228.65   $228.60  
  Purchase #3 $170.32   8.124%   $184.1568   $184.16   $184.15   $184.20  
  Purchase #4 $44.78   7.265%   $48.0333   $48.03   $48.05   $48.00  
  Purchase #5 $223.59   11.414%   $249.1106   $249.11   $249.10   $249.10  
  Purchase #6 $28.57   6.718%   $30.4893   $30.49   $30.50   $30.50  
  Purchase #7 $47.94   12.851%   $54.1008   $54.10   $54.10   $54.10  
  7 purchase totals = $965.53       $1,057.7914   $1,057.79   $1,057.80   $1,057.80