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 $61.78   12.488%   $69.4951   $69.50   $69.50   $69.50  
  Purchase #2 $206.77   4.652%   $216.3889   $216.39   $216.40   $216.40  
  Purchase #3 $214.58   9.640%   $235.2655   $235.27   $235.25   $235.30  
  Purchase #4 $221.72   4.482%   $231.6575   $231.66   $231.65   $231.70  
  Purchase #5 $120.39   11.799%   $134.5948   $134.59   $134.60   $134.60  
  Purchase #6 $8.90   8.479%   $9.6546   $9.65   $9.65   $9.70  
  Purchase #7 $114.28   11.190%   $127.0679   $127.07   $127.05   $127.10  
  7 purchase totals = $948.42       $1,024.1243   $1,024.13   $1,024.10   $1,024.30