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 $144.25   5.758%   $152.5559   $152.56   $152.55   $152.60  
  Purchase #2 $245.90   8.872%   $267.7162   $267.72   $267.70   $267.70  
  Purchase #3 $66.91   11.430%   $74.5578   $74.56   $74.55   $74.60  
  Purchase #4 $115.53   13.771%   $131.4396   $131.44   $131.45   $131.40  
  Purchase #5 $238.64   8.232%   $258.2848   $258.28   $258.30   $258.30  
  Purchase #6 $127.67   5.761%   $135.0251   $135.03   $135.05   $135.00  
  Purchase #7 $114.55   8.853%   $124.6911   $124.69   $124.70   $124.70  
  7 purchase totals = $1,053.45       $1,144.2705   $1,144.28   $1,144.30   $1,144.30