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 $217.86   10.631%   $241.0207   $241.02   $241.00   $241.00  
  Purchase #2 $54.45   12.270%   $61.131   $61.13   $61.15   $61.10  
  Purchase #3 $230.94   9.404%   $252.6576   $252.66   $252.65   $252.70  
  Purchase #4 $194.33   13.288%   $220.1526   $220.15   $220.15   $220.20  
  Purchase #5 $172.77   11.493%   $192.6265   $192.63   $192.65   $192.60  
  Purchase #6 $206.38   3.153%   $212.8872   $212.89   $212.90   $212.90  
  Purchase #7 $241.51   7.108%   $258.6765   $258.68   $258.70   $258.70  
  7 purchase totals = $1,318.24       $1,439.1521   $1,439.16   $1,439.20   $1,439.20