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 $167.66   11.392%   $186.7598   $186.76   $186.75   $186.80  
  Purchase #2 $55.99   8.273%   $60.6221   $60.62   $60.60   $60.60  
  Purchase #3 $32.25   8.776%   $35.0803   $35.08   $35.10   $35.10  
  Purchase #4 $239.67   7.674%   $258.0623   $258.06   $258.05   $258.10  
  Purchase #5 $5.65   10.474%   $6.2418   $6.24   $6.25   $6.20  
  Purchase #6 $218.94   13.453%   $248.394   $248.39   $248.40   $248.40  
  Purchase #7 $166.75   11.252%   $185.5127   $185.51   $185.50   $185.50  
  7 purchase totals = $886.91       $980.6730   $980.66   $980.65   $980.70