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 $207.48   13.546%   $235.5852   $235.59   $235.60   $235.60  
  Purchase #2 $224.31   7.769%   $241.7366   $241.74   $241.75   $241.70  
  Purchase #3 $218.64   13.554%   $248.2745   $248.27   $248.25   $248.30  
  Purchase #4 $228.59   8.483%   $247.9813   $247.98   $248.00   $248.00  
  Purchase #5 $111.58   9.724%   $122.43   $122.43   $122.45   $122.40  
  Purchase #6 $195.64   12.229%   $219.5648   $219.56   $219.55   $219.60  
  Purchase #7 $218.72   8.521%   $237.3571   $237.36   $237.35   $237.40  
  7 purchase totals = $1,404.96       $1,552.9295   $1,552.93   $1,552.95   $1,553.00