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 $90.92   5.431%   $95.8579   $95.86   $95.85   $95.90  
  Purchase #2 $44.85   9.277%   $49.0107   $49.01   $49.00   $49.00  
  Purchase #3 $172.88   6.832%   $184.6912   $184.69   $184.70   $184.70  
  Purchase #4 $42.48   8.299%   $46.0054   $46.01   $46.00   $46.00  
  Purchase #5 $115.94   5.416%   $122.2193   $122.22   $122.20   $122.20  
  Purchase #6 $184.31   13.301%   $208.8251   $208.83   $208.85   $208.80  
  Purchase #7 $147.94   8.317%   $160.2442   $160.24   $160.25   $160.20  
  7 purchase totals = $799.32       $866.8538   $866.86   $866.85   $866.80