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 $64.95   6.195%   $68.9737   $68.97   $68.95   $69.00  
  Purchase #2 $53.45   12.428%   $60.0928   $60.09   $60.10   $60.10  
  Purchase #3 $58.55   8.216%   $63.3605   $63.36   $63.35   $63.40  
  Purchase #4 $147.46   10.376%   $162.7604   $162.76   $162.75   $162.80  
  Purchase #5 $35.72   13.611%   $40.5818   $40.58   $40.60   $40.60  
  Purchase #6 $224.30   6.562%   $239.0186   $239.02   $239.00   $239.00  
  Purchase #7 $145.38   4.196%   $151.4801   $151.48   $151.50   $151.50  
  7 purchase totals = $729.81       $786.2679   $786.26   $786.25   $786.40