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 $58.36   6.312%   $62.0437   $62.04   $62.05   $62.00  
  Purchase #2 $143.79   3.843%   $149.3158   $149.32   $149.30   $149.30  
  Purchase #3 $249.49   13.479%   $283.1188   $283.12   $283.10   $283.10  
  Purchase #4 $57.48   8.205%   $62.1962   $62.20   $62.20   $62.20  
  Purchase #5 $107.70   13.501%   $122.2406   $122.24   $122.25   $122.20  
  Purchase #6 $163.50   11.320%   $182.0082   $182.01   $182.00   $182.00  
  Purchase #7 $55.84   11.194%   $62.0907   $62.09   $62.10   $62.10  
  7 purchase totals = $836.16       $923.0140   $923.02   $923.00   $922.90