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 $46.59   13.299%   $52.786   $52.79   $52.80   $52.80  
  Purchase #2 $119.46   11.409%   $133.0892   $133.09   $133.10   $133.10  
  Purchase #3 $198.58   7.233%   $212.9433   $212.94   $212.95   $212.90  
  Purchase #4 $103.77   6.119%   $110.1197   $110.12   $110.10   $110.10  
  Purchase #5 $205.86   6.378%   $218.9898   $218.99   $219.00   $219.00  
  Purchase #6 $227.68   10.751%   $252.1579   $252.16   $252.15   $252.20  
  Purchase #7 $47.94   10.659%   $53.0499   $53.05   $53.05   $53.00  
  7 purchase totals = $949.88       $1,033.1358   $1,033.14   $1,033.15   $1,033.10