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 $51.56   13.764%   $58.6567   $58.66   $58.65   $58.70  
  Purchase #2 $175.39   13.792%   $199.5798   $199.58   $199.60   $199.60  
  Purchase #3 $59.35   4.834%   $62.219   $62.22   $62.20   $62.20  
  Purchase #4 $147.76   8.417%   $160.197   $160.20   $160.20   $160.20  
  Purchase #5 $140.64   10.691%   $155.6758   $155.68   $155.70   $155.70  
  Purchase #6 $135.54   4.647%   $141.8385   $141.84   $141.85   $141.80  
  Purchase #7 $41.92   5.160%   $44.0831   $44.08   $44.10   $44.10  
  7 purchase totals = $752.16       $822.2499   $822.26   $822.30   $822.30