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 $218.37   13.681%   $248.2452   $248.25   $248.25   $248.20  
  Purchase #2 $224.50   5.351%   $236.513   $236.51   $236.50   $236.50  
  Purchase #3 $219.48   9.836%   $241.0681   $241.07   $241.05   $241.10  
  Purchase #4 $246.99   6.221%   $262.3552   $262.36   $262.35   $262.40  
  Purchase #5 $16.96   12.233%   $19.0347   $19.03   $19.05   $19.00  
  Purchase #6 $226.80   13.362%   $257.105   $257.11   $257.10   $257.10  
  Purchase #7 $57.40   8.240%   $62.1298   $62.13   $62.15   $62.10  
  7 purchase totals = $1,210.50       $1,326.4510   $1,326.46   $1,326.45   $1,326.40