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 $60.91   13.260%   $68.9867   $68.99   $69.00   $69.00  
  Purchase #2 $151.62   4.667%   $158.6961   $158.70   $158.70   $158.70  
  Purchase #3 $124.32   8.507%   $134.8959   $134.90   $134.90   $134.90  
  Purchase #4 $99.38   8.771%   $108.0966   $108.10   $108.10   $108.10  
  Purchase #5 $130.90   3.554%   $135.5522   $135.55   $135.55   $135.60  
  Purchase #6 $104.52   9.843%   $114.8079   $114.81   $114.80   $114.80  
  Purchase #7 $200.78   5.374%   $211.5699   $211.57   $211.55   $211.60  
  7 purchase totals = $872.43       $932.6053   $932.62   $932.60   $932.70