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 $246.59   5.583%   $260.3571   $260.36   $260.35   $260.40  
  Purchase #2 $155.80   9.417%   $170.4717   $170.47   $170.45   $170.50  
  Purchase #3 $49.58   6.838%   $52.9703   $52.97   $52.95   $53.00  
  Purchase #4 $232.85   6.611%   $248.2437   $248.24   $248.25   $248.20  
  Purchase #5 $164.85   11.685%   $184.1127   $184.11   $184.10   $184.10  
  Purchase #6 $25.71   6.591%   $27.4045   $27.40   $27.40   $27.40  
  Purchase #7 $210.43   6.182%   $223.4388   $223.44   $223.45   $223.40  
  7 purchase totals = $1,085.81       $1,166.9988   $1,166.99   $1,166.95   $1,167.00